Image pickup apparatus with lens control apparatus and focusing lens control

ABSTRACT

A lens control apparatus and an image pickup apparatus each of which, during a magnification varying operation in an inner focus type of lens system, predicts a destination position to be reached by a variator lens after a predetermined time period, calculates a speed at which to move a focusing lens to a correction position of a focal plane relative to the predicted position of the variator lens, and controls the focusing lens.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an image pickup apparatus such as avideo camera and, more particularly, to an arrangement which is suitablefor use in an apparatus using an inner focus type of lens system.

2. Description of Related Art

FIG. 2 is a view showing a simple arrangement of an inner focus type oflens system which has conventionally been used. The arrangement shown inFIG. 2 includes a fixed first lens group 101, a second lens group(variator lens) 102 for performing a magnification varying operation, aniris 103, a fixed third lens group 104, a fourth lens group (focusinglens) 105 having both a focus adjusting function and a so-calledcompensation function which compensates for a movement of a focal planedue to a magnification varying operation, and an image pickup element106.

As is already known, in the lens system which is arranged as shown inFIG. 2, since the focusing lens 105 has both the compensation functionand the focus adjusting function, the position of the focusing lens 105for forming an in-focus image on an image pickup surface of the imagepickup element 106 differs for different subject distances even in thecase of the same focal length. If a variation in the position of thefocusing lens 105 for forming an in-focus image on the image pickupsurface of the image pickup element 106 is continuously plotted againstdifferent subject distances for different focal lengths, the resultantloci are as shown in FIG. 3. During a magnification varying operation,zooming free of defocusing is enabled by selecting a locus from the locishown in FIG. 3 according to the subject distance and moving thefocusing lens 105 along the selected locus.

A front-lens focus type of lens system is provided with a compensatorlens which is independent of a variator lens, and the variator lens andthe compensator lens are connected to each other by a mechanical camring. Accordingly, if a knob for manual zooming is provided on the camring so that the focal length can be manually varied, no matter how fastthe knob may be moved, the cam ring rotates in accordance with themovement of the knob, and the variator lens and the compensator lensmove along a cam groove in the cam ring. Therefore, as long as thefocusing lens is in focus, the above operation does not causedefocusing.

In the control of the above-described inner focus type of lens system,it is general practice to previously store a plurality of pieces oflocus information such as those shown in FIG. 3 in a lens controlmicrocomputer in a particular form, select a locus according to therelative position between the focusing lens and the variator lens, andperform zooming while tracing the selected locus. In such control, it isnecessary to read the position of each of the focusing lens and thevariator lens with a certain degree of accuracy, because the position ofthe focusing lens relative to the position of the variator lens is readfrom a storage element and applied to lens control.

As can be seen from FIG. 3 as well, if the variator lens moves at ornear a uniform speed, the inclination of the locus of the focusing lenssuccessively varies with a variation in the focal length. This indicatesthat the moving speed and direction of the focusing lens varysuccessively. In other words, an actuator for the focusing lens, if itis a stepping motor, needs to make a highly accurate speed response of 1Hz up to several hundred Hz.

It is becoming general practice to use a stepping motor for the focusinglens group of the inner focus type of lens system as an actuator whichsatisfies the above requirement. The stepping motor is capable ofrotating in complete synchronism with a step pulse outputted from a lenscontrol microcomputer or the like and showing a constant stepping angleper pulse, so that the stepping motor can realize high speed response,high stopping accuracy and high positional accuracy. Furthermore, thestepping motor provides the advantage that since its rotating angle perstep pulse is constant, the step pulse can be used for an increment typeof encoder and a special position encoder is not needed.

As described above, if a magnification varying operation is to becarried out while keeping an in-focus state by using such a steppingmotor, it is necessary to previously store the locus information shownin FIG. 3 in the lens control microcomputer or the like in a particularform (the loci themselves may be stored or a function which uses lenspositions as variables may be stored), and read locus informationaccording to the position or the moving speed of the variator lens andmove the focusing lens on the basis of the read locus information.

FIG. 4 is a view aiding in explaining a locus tracing method which haspreviously been proposed. In FIG. 4, Z0, Z1, Z2, . . . , Z6 indicate theposition of the variator lens, a0, a1, a2, . . . , a6 and b0, b1, b2, .. . , b6 respectively indicate representative loci stored in the lenscontrol microcomputer, and p0, p1, p2, . . . , p6 indicate a locuscalculated on the basis of the two loci. An equation for calculatingthis locus is shown below:

p(n+1)=(|p(n)−a(n)|/|b(n)−a(n)|)×|b(n+1)−a(n+1)|+a(n+1).  (1)

According to Equation (1), for example, if the focusing lens is locatedat the point p0 in FIG. 4, the ratio in which the point p0 internallydivides a line segment b0-a0 is obtained, and a point which internallydivides a line segment b1-a1 in accordance with that ratio is determinedas p1. The standard moving speed of the focusing lens required to keepan in-focus state can be found from the p1−p0 positional difference andthe time required for the variator lens to move from Z0 to Z1.

A case in which the stop position of the variator lens is not limitedonly to boundaries having stored representative locus data will bedescribed below with reference to FIG. 5.

FIG. 5 is a view aiding in explaining a method of interpolating theposition of the variator lens. FIG. 5 is an extracted portion of FIG. 4(a dashed-line portion in FIG. 4) and shows a case in which the variatorlens can be stopped at an arbitrary stop position. In FIG. 5, thevertical and horizontal axes respectively represent the position of thefocusing lens and the position of the variator lens. Letting Z0, Z1, . .. , Zk−1, Zk, . . . Zn represent the position of the variator lens, thecorresponding positions of the focusing lens for different subjectdistances, i.e., the representative locus positions (the position of thefocusing lens relative to the position of the variator lens) stored in alens control microcomputer are as follows:

a0, a1, . . . , ak−1, ak, . . . an,

b0, b1, . . . , bk−1, bk, . . . bn.

If it is now assumed that the position of the variator lens is Zx whichis not a zoom boundary position and that the position of the focusinglens is px, positions ax and bx are obtained as follows:

ax=ak−(Zk−Zx)×((ak−ak−1)/(Zk−Zk−1)),  (2)

bx=bk−(Zk−Zx)×((bk−bk−1)/(Zk−Zk−1)).  (3)

Specifically, in accordance with an internal ratio which is obtainedfrom the current position of the variator lens and two adjacent oppositezoom boundary positions (for example, Zk and Zk−1 in FIG. 5), locus datacorresponding to the same subject distance are selected from among fourstored representative locus data (ak, ak−1, bk, bk−1 in FIG. 5) and areinternally divided by the internal ratio shown by the above equation(1), whereby ax and bx can be obtained.

Then, in accordance with an internal ratio which is obtained from ax, pxand bx, the locus data corresponding to the same focal length, which areselected from among the four stored representative locus data (ak, ak−1,bk, bk−1 in FIG. 5), are internally divided by the internal ratio shownby the above equation (1), whereby pk and pk−1 can be obtained.Furthermore, during zooming from the wide-angle end toward the telephotoend, the moving speed of the focusing lens required to keep an in-focusstate can be found from the difference between the target focusing-lensposition pk and the current focusing-lens position px and the timerequired for the variator lens to move from Zx to Zk.

Furthermore, during zooming from the telephoto end toward the wide-angleend, the standard moving speed of the focusing lens required to keep anin-focus state can be found from the difference between the targetfocusing-lens position pk−1 and the current focusing-lens position pxand the time required for the variator lens to move from Zx to Zk−1. Theabove-described locus tracing method has been devised.

As can be seen from FIG. 3, if the variator lens moves from thetelephoto end toward the wide-angle end in the direction in whichdivergent loci gradually converge, an in-focus state can be maintainedby the above-described locus tracing method. However, if the variatorlens moves from the wide-angle end toward the telephoto end, it isimpossible to determine which locus should be traced by the focusinglens which is located at a point on convergent loci, so that an in-focusstate cannot be maintained by the above-described locus tracing method.

FIGS. 6(A) and 6(B) are views aiding in explaining one example of alocus tracing method which has previously been devised to solve theabove-described problem. In each of FIGS. 6(A) and 6(B), the horizontalaxis represents the position of the variator lens, and the vertical axisof FIG. 6(A) represents the level of a high-frequency component(sharpness signal) of a video signal which is an AF evaluation signal,whereas the vertical axis of FIG. 6(B) represents the position of thefocusing lens.

In FIG. 6(B), it is assumed that a locus 604 is an in-focus cam locus tobe used for zooming relative to a certain subject. It is also assumedthat the standard moving speed for in-focus cam locus tracing on thewide-angle side of a zoom position 606 (Z14) is positive (the focusinglens moves toward its closest-distance end), and that the standardmoving speed for in-focus cam locus tracing on the telephoto side of thezoom position 606 is negative (the focusing lens moves toward itsinfinity end). If the focusing lens traces the cam locus 604 whilemaintaining an in-focus state, the magnitude of the AF evaluation signalbecomes as shown at 601 in FIG. 6(A). It is generally known that zoomingwhich maintains an in-focus state exhibits an AF evaluation signal levelwhich has an approximately constant value.

In FIG. 6(B), Vf0 indicates the standard moving speed of the focusinglens which traces the in-focus cam locus 604 during zooming, and Vfindicates an actual moving speed of the focusing lens. If zooming isperformed while varying its speed with respect to the speed Vf0 whichtraces the locus 604, a zigzag locus like a locus 605 is obtained. Inthis case, the sharpness signal level varies in such a manner that hillsand valleys repeatedly occur like a locus 603.

The magnitude of the sharpness signal 603 reaches its maximum at eachposition where the loci 604 and 605 cross each other (even-numberedpoints among Z0, Z1, . . . , Z16), whereas the magnitude of thesharpness signal 603 reaches its minimum at each position where themoving-direction vector of the locus 605 switches over (odd-numberedpoints among Z0, Z1, . . . , Z16). The sharpness signal 603 has aminimum value 602, and if the minimum value 602 is set as a level TH1and the moving-direction vector of the locus 605 is switched over eachtime the magnitude of the sharpness signal 603 becomes equal to thelevel TH1, the moving direction of the focusing lens after switchovercan be set to a direction closer to the locus 604.

In other words, each time an image is defocused by the differencebetween the levels 601 and 602 (TH1) of the AF evaluation signal, if themoving direction and the moving speed of the focusing lens arecontrolled to decrease the amount of defocusing, it is possible toeffect zooming with the amount of defocusing reduced.

By using the above-described method, in the case of zooming from thewide-angle end toward the telephoto end in which convergent cam locigradually diverge as shown in FIG. 3, even if the standard moving speedVf0 of the focusing lens which maintains an in-focus state is notoptimum for a target subject distance, it is possible to select a locuscapable of preventing the AF evaluation signal level from falling belowthe minimum value 602 (TH1), i.e., preventing occurrence of not lessthan a certain amount of defocusing, by repeating a switchover operationlike the locus 605 in accordance with a variation in the AF evaluationsignal level while controlling the moving speed Vf of the focusing lenswith respect to the standard moving speed (calculated by using p(n+1)obtained from Equation (1)). Furthermore, regarding the amount ofdefocusing, if the level TH1 is appropriately set, it is possible torealize zooming during which defocusing apparently is not observed.

Letting Vf⁺ and Vf⁻ be a positive correction speed and a negativecorrection speed, respectively, the moving speed Vf of the focusing lensis determined as:

Vf=Vf 0+Vf ⁺,  (4)

Vf=Vf 0+Vf ⁻.  (5)

At this time, to prevent the correction speeds Vf⁺ and Vf⁻ fromdeviating in either correction direction when a focus locus to be tracedis selected, the correction speeds Vf⁺ and Vf⁻ are determined so thatthe internal angle made by the two direction vectors of the moving speedVf which are obtained from the above equations (4) and (5) is dividedinto two equal angles by the direction vector of the standard movingspeed Vf0. In addition, another method has been devised which isintended to improve the accuracy of selection of a focus locus to betraced, by varying the increase-decrease period of the sharpness signalby varying the amount of correction due to a correction speed accordingto the kind or state of a subject, the focal length or the depth offield.

In general, the above-described control for the magnification varyingoperation is performed in synchronism with a vertical synchronizingsignal because a video signal from an image pickup element is used todetect focus.

FIG. 7 shows a control flowchart of a conventional example of lenscontrol performed by a lens control microcomputer. Step S1 indicates thestart of processing. Step S2 is an initial setting routine for executingthe processing of initializing various ports and a RAM in the lenscontrol microcomputer.

Step S3 is a routine for intercommunication with a system controlmicrocomputer which controls the operating system of a camera body. InStep S3, when the lens control microcomputer receives zoom-switch-unitinformation from a zoom switch unit operated by a photographer, the lenscontrol microcomputer provides magnification-varying-operationinformation, such as the position of a zooming lens, to inform thephotographer that a zooming operation is being executed, and theinformation is given to the photographer through a display or the like.

Step S4 is an AF processing routine for performing the processing ofmaking automatic adjustment of focus according to a variation in the AFevaluation signal.

Step S5 is a zooming processing routine for processing a compensationoperation for maintaining an in-focus state during a magnificationvarying operation.

By the above-described method, calculations are performed on a standarddriving direction and a standard moving speed of a focusing lens whichtraces a cam locus such as that shown in FIG. 4.

Step S6 is a routine for making selection from among the drivingdirections and the driving speeds for the variator lens and the focusinglens which have been calculated in the processing routines of Steps S4and S55, according to whether to execute an AF operation or amagnification varying operation, and executing setting so as not todrive the lenses beyond their respective telephoto ends, wide-angleends, closest-distance ends or infinity ends all of which are set bysoftware so as not to prevent the lenses from coming into contact withend portions of their respective mechanical portions.

In Step S7, the lens control microcomputer outputs control signals tomotor drivers according to the driving directions and the driving speedsfor the variator lens and the focusing lens which have been determinedin Step S6, thereby controlling the respective motors to drive or stopthe variator lens and the focusing lens.

After the completion of the processing of Step S7, the process returnsto Step S3.

The entire processing shown in FIG. 7 is executed in synchronism witheach vertical synchronizing period (in the processing of Step S3, theprocess waits for the arrival of the next vertical synchronizingsignal).

However, in the case of a recent type of video camera having a farfaster zooming speed, for example, the variator lens may often move froma position Z4 to a position Z6 (shown in FIG. 4) within the time of onevertical synchronizing period. During this time, if the lens controlprocessing of FIG. 7 is performed in synchronism with the verticalsynchronizing period, the standard moving speed of the focusing lensremains the speed at which the focusing lens is moving from p4 to p5,and the updating of the standard moving speed is not performed until thevariator lens reaches the position Z6. Accordingly, when the position ofthe variator lens is Z6, the focusing lens lies at a point p6′ on a linewhich rectilinearly extends from the line p4-p5 in FIG. 4, so thatdefocusing occurs by the difference between p6′ and p6 and accuratetracing of a cam locus cannot be performed during zooming.

To solve the above-described problem, a method based on the processingroutine shown in FIG. 8 has been proposed. In this method, the standardmoving speed of a focusing lens is calculated by a plurality of times(twice, in the example shown in FIG. 8) within one verticalsynchronizing period so that the occurrence of defocusing is prevented.In FIG. 8, the processing of Steps S11 to S17 is similar to that ofSteps S1 to S7 of FIG. 7.

After the completion of the processing of Step S17, the process waitsfor a predetermined period of time in Step S18 until the middle point ofthe vertical synchronizing period. After the lapse of the predeterminedtime, if it is determined in Step S19 that zooming is being executed, itis determined that the position of the variator lens has been updated,and processing similar to the processing of Steps S15 to S17 is againexecuted.

In Step S20, the driving directions for the variator lens and thefocusing lens as well as the standard moving speed for the focusing lensare again calculated, and in Step S21, selection is made from among thedriving directions and the driving speeds for the variator lens and thefocusing lens which have been calculated in Step S20. In Step S22, theselected driving directions and speeds are output to the respectivemotor drivers to execute lens control, and the process then returns toStep S13.

If it is determined in Step S19 that zooming is not being executed, theprocess returns to Step S13 and waits for the next operation.

The entire processing shown in FIG. 8 is executed in synchronism withthe vertical synchronizing period, and in the processing of Step S13,the process waits for the arrival of the next vertical synchronizingsignal.

If the standard moving speed of the focusing lens is calculated onlyonce within one vertical synchronizing period during zooming, thefocusing lens reaches the point p6′ at a focusing speed equivalent tothe inclination of the line p4-p5 during the movement of the variatorlens from Z4 to Z6 (in FIG. 4) within one vertical synchronizing period.In contrast, in the above-described method, since the standard movingspeed of the focusing lens is calculated twice within one verticalsynchronizing period, the focusing lens reaches the point p5 at afocusing speed equivalent to the inclination of the line p4-p5 duringthe first half of one vertical synchronizing period, and moves past thepoint p5 at a focusing speed equivalent to the inclination of the linep5-p6 during the second half of the one vertical synchronizing period,so that the focusing lens can reach the point p6 after the one verticalsynchronizing period. Accordingly, it is possible to realize accuratetracing of a cam locus and prevention of occurrence of defocusing.

However, in the above-described conventional example, since the standardmoving speed of the focusing lens is calculated by a plurality of timesduring one vertical synchronizing period so that defocusing is preventedduring the tracing of a cam locus, the load on the lens controlmicrocomputer becomes large during high-speed zooming. Specifically, theconventional example needs a microcomputer having a fast processingspeed which is capable of executing a calculation of the standard movingspeed by a plurality of times during one vertical synchronizing period,and a video camera using such a microcomputer becomes expensive for auser.

The standard moving speed for the focusing lens which is calculated bythe above-described cam locus tracing method is obtained by calculatinga destination target position relative to a zoom-lens position havingrepresentative locus data indicative of the closest distance to thecurrent zoom position Zx, i.e., the boundary position (Zk−1 or Zk) inthe zoom area shown in FIG. 5. Accordingly, there is a case in which theperiod of time required for the variator lens to move from Zx to Zk−1 orZk is short because of the timing of executing the calculation. At thistime, a large calculation error occurs in the division computation ((themoving distance of the focusing lens)÷(the time period of movement ofthe variator lens)) required to calculate the standard moving speed, sothat the problem that an in-focus locus cannot be accurately traced alsoarises.

A number of problems which occur in the above-described conventional camlocus tracing method will be further described below with reference toan example in which a linear motor is used as a lens driving actuator.Linear motors have recently been used in more and more products becauseof their superior high-speed performance.

In general, in a system in which a linear motor such as a voice coilmotor is used as a focusing motor, a position encoder for detecting theposition of a focusing lens is disposed to form a feedback loop so thata deviation signal between the output signal of the position encoder anda target position signal outputted from a control circuit approacheszero, and the driving speed of the motor is determined by the responsecharacteristics of the feedback loop.

Accordingly, the focus correcting operation of the focusing lens duringthe tracing of a cam locus is effected not by a control method based onthe driving direction and the driving speed but by a control methodusing a destination target position as a parameter. Accordingly, duringthe tracing of a cam locus, the destination target position to bereached by the focusing lens corresponds to the position px obtainedfrom the above-described equation (1).

However, in a recent type of video camera having a far faster zoomingspeed, for example, in a case where the variator lens moves from theposition Z4 to the position Z6 (shown in FIG. 4) within the time of onevertical synchronizing period, if the lens control processing of FIG. 7is performed in synchronism with the vertical synchronizing period as inthe case of the above-described conventional example, the point p5 at azoom boundary having cam locus data is calculated as a target position.Even if the variator lens proceeds to Z6, the updating of the targetposition is not performed, and because of loop control, the position ofthe focusing lens remains p5 (p6″ in FIG. 4) and defocusing occurs.

In particular, both the time required for the variator lens to move bythe distance difference between the current position of the variatorlens and the zoom boundary position and the time required for thefocusing lens to move by the distance difference between a calculatedtarget trace position and the current position of the focusing lens varydepending on computation timing and zooming speed. Accordingly, if thefocusing lens is to be located at a target position when the variatorlens reaches a boundary, it is necessary to execute complicatedprocessing extremely difficult to realize.

BRIEF SUMMARY OF THE INVENTION

One object of the present invention is to provide an image pickupapparatus and an image pickup method both of which make it possible toinexpensively realize comfortable and superior zooming performancewithout the need to produce loads on a processing microcomputer andirrespective of the zooming speed of a magnification varying operationand the kind of focusing motor.

Another object of the present invention is to provide an image pickupapparatus capable of effecting high-performance zooming free ofdefocusing even during high-speed zooming.

Another object of the present invention is to provide an image pickupapparatus and a lens control apparatus both of which are capable ofpreventing defocusing from occurring when a zooming operation stops.

To achieve the above objects, in accordance with one aspect of thepresent invention, there is provided an image pickup apparatus whichcomprises a first lens group for performing a magnification varyingoperation, a second lens group for correcting a movement of a focalplane during a movement of the first lens group, driving means forrespectively driving the first lens group and the second lens group, astorage medium for storing, according to a subject distance, an in-focusposition of the second lens group relative to a position of the firstlens group, predicting means for predicting a destination position to bereached by the first lens group after a predetermined time period,during the magnification varying operation, and control means forperforming correction of focus by calculating a standard moving speed ofthe second lens group for correcting a movement of the focal plane withrespect to the predicted destination position, according to informationstored in the storage medium, and driving the second lens group at thestandard moving speed.

In accordance with another aspect of the present invention, there isprovided an image pickup apparatus which comprises a first lens groupfor performing a magnification varying operation, a second lens groupfor correcting a movement of a focal plane during a movement of thefirst lens group, driving means for respectively driving the first lensgroup and the second lens group, a storage medium for storing, accordingto a subject distance, an in-focus position of the second lens grouprelative to a position of the first lens group, focus detecting meansfor outputting a focus signal, predicting means for predicting adestination position to be reached by the first lens group after apredetermined time period, during the magnification varying operation,and control means for calculating a standard moving speed of the secondlens group for correcting a movement of the focal plane with respect tothe predicted destination position, according to information stored inthe storage medium, and driving the second lens group while varying thestandard moving speed according to an increase or decrease in the focussignal.

In accordance with another aspect of the present invention, there isprovided an image pickup apparatus which comprises a first lens groupfor performing a magnification varying operation, a second lens groupfor correcting a movement of a focal plane during a movement of thefirst lens group, driving means for respectively driving the first lensgroup and the second lens group, a storage medium for storing, accordingto a subject distance, an in-focus position of the second lens grouprelative to a position of the first lens group, predicting means forpredicting a destination position to be reached by the first lens groupafter a predetermined time period, during the magnification varyingoperation, calculating means for finding a correction position of thesecond lens group for correcting a movement of the focal plane withrespect to the destination position, according to information stored inthe storage medium, and control means for controlling a position of thesecond lens group so that the second lens group reaches the correctionposition after the predetermined time period.

In accordance with another aspect of the present invention, there isprovided a lens control apparatus which comprises a first lens group forperforming a magnification varying operation, a second lens group forcorrecting a movement of a focal plane during a movement of the firstlens group, driving means for respectively driving the first lens groupand the second lens group, a storage medium for storing, according to asubject distance, an in-focus position of the second lens group relativeto a position of the first lens group, extracting means for extracting afocus signal from a signal of an image picked up by image pickup means,predicting means for predicting a destination position to be reached bythe first lens group after a predetermined time period, during themagnification varying operation, calculating means for finding acorrection position of the second lens group for correcting a movementof the focal plane with respect to the destination position, accordingto information stored in the storage medium, correction positionchanging means for changing the correction position according to anincrease or decrease in the focus signal, and control means forcontrolling a position of the second lens group so that the second lensgroup reaches the changed correction position after the predeterminedtime period.

Another object of the present invention is to provide a lens controlapparatus capable of effecting high-speed zooming free of defocusingirrespective of the kind of lens driving actuator.

Another object of the present invention is to provide a lens controlapparatus capable of effecting speed control and smooth driving in aposition servo system driving by feedback loop.

To achieve the above objects, in accordance with one aspect of thepresent invention, there is provided a lens control apparatus whichcomprise a movable part which is movable along an optical axis forperforming focus adjustment, an actuator for driving the movable part,position-of-movable-part detecting means for detecting a position of themovable part, focus control means for determining a state of focus andsupplying a driving signal which causes the movable part to move towardan in-focus position, according to the determined state of focus, andposition control means for performing position control of the movablepart via the actuator by updating the driving signal by a plurality oftimes during a predetermined time period so that an average moving speedof the movable part during the predetermined time period becomes apredetermined speed.

Another object of the present invention is to realize a lens controlsystem capable of effecting highly accurate speed control even if thelens control system is used with a position-feedback-system actuatorsuch as a linear motor or a voice coil motor.

The above and other objects, features and advantages of the presentinvention will become apparent from the following detailed descriptionof preferred embodiments of the present invention, taken in conjunctionwith the accompanying drawings.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

FIG. 1 is a block diagram showing the entire arrangement of a firstembodiment of the present invention;

FIG. 2 is a schematic view showing the arrangement of an inner focustype of lens system which has heretofore been used;

FIG. 3 is a diagram showing the relationship between the position of avariator lens and the position of a focusing lens;

FIG. 4 is a view showing one example of a locus tracing method which haspreviously been devised;

FIG. 5 is a view showing an interpolation method relative to thedirection of the position of a variator lens;

FIGS. 6(A) and 6(B) are views aiding in describing one example of alocus tracing method which has previously been devised;

FIG. 7 is a flowchart showing a conventional lens control sequence;

FIG. 8 is a flowchart showing a conventional lens control sequence;

FIG. 9 is a flowchart showing a control sequence according to a firstembodiment;

FIG. 10 is a flowchart showing a control sequence according to the firstembodiment;

FIG. 11 is a flowchart showing a control sequence according to the firstembodiment;

FIG. 12 is a view showing a data table of cam locus information used inthe first embodiment;

FIG. 13 is a flowchart showing a control sequence according to a secondembodiment of the present invention;

FIG. 14 is a view aiding in describing a computation according to thesecond embodiment;

FIG. 15 is a block diagram showing a third embodiment of the presentinvention;

FIGS. 16(A) and 16(B) are schematic views of a linear motor according tothe third embodiment;

FIG. 17 is a flowchart showing a control sequence according to the thirdembodiment;

FIG. 18 is a block diagram showing the arrangement of an image pickupapparatus according to a fourth embodiment of the present invention;

FIG. 19 is a flowchart aiding in describing the details of high-climbingdriving processing in the fourth embodiment;

FIG. 20 is a flowchart aiding in describing the processing of generatinga driving target signal to be supplied from a microcomputer to acomparing circuit in the fourth embodiment;

FIG. 21 is a flowchart aiding in describing the details of wobblingoperation processing in a fifth embodiment of the present invention;

FIG. 22 is a flowchart aiding in describing position control processingfor the focusing lens during a wobbling operation;

FIG. 23 is a view aiding in describing the wobbling operation and itsamplitude;

FIG. 24 is a flowchart aiding in describing zooming operation processingto be performed on a control cycle of one vertical synchronizing periodin a sixth embodiment of the present invention;

FIG. 25 is a flowchart aiding in describing compensation operationprocessing relative to a movement of the variator lens;

FIG. 26 is a flowchart aiding in describing zooming-speed resettingprocessing in a seventh embodiment of the present invention;

FIG. 27 is a flowchart aiding in describing the processing ofdetermining whether to execute a forced movement of the focusing lens inan eighth embodiment of the present invention;

FIG. 28 is a flowchart aiding in describing the processing of resettinga forced movement flag indicative of the forced movement of the focusinglens;

FIG. 29 is a flowchart aiding in describing compensation operationprocessing relative to a movement of the focusing lens in a ninthembodiment of the present invention;

FIG. 30 is a block diagram showing the construction of a general imagepickup apparatus;

FIG. 31 is a flowchart aiding in describing zooming operation processingin the image pickup apparatus using a linear motor;

FIG. 32 is a flowchart aiding in describing the details of locusparameter calculating processing in the zooming operation processing;

FIG. 33 is a flowchart aiding in describing the details of zoom areacalculating processing in the locus parameter calculating processing;

FIG. 34 is a flowchart aiding in describing the details of variator-lensdriving processing in the zooming operation processing;

FIG. 35 is a view aiding in describing a data table of cam locusinformation; and

FIG. 36 is a flowchart aiding in describing autofocus operationprocessing.

DETAILED DESCRIPTION OF THE INVENTION

Preferred embodiments of an image pickup apparatus according to thepresent invention will be described below in detail with reference tothe accompanying drawings.

First Embodiment

FIG. 1 is a block diagram showing the entire arrangement of a firstembodiment of the present invention. The arrangement shown in FIG. 1includes a fixed front lens group 101, a second lens group (variatorlens) 102 for performing a magnification varying operation, an iris 103,a fixed third lens group 104, and a fourth lens group (focusing lens)105 which has both a compensation function and a focusing function.These constituent elements 101 to 105 constitute an inner focus type oflens system. Image light which has passed through this lens system isfocused on an image pickup surface of an image pickup element 106 andconverted into a video signal by photoelectric conversion. The videosignal is amplified to an optimum level by an amplifier 107, and theamplified video signal is inputted to a camera signal processing circuit108 and converted into a standard television signal (video signal).

The video signal amplified by the amplifier 107 is sent to both an iriscontrol circuit 121 and an AF signal processing circuit 109. The iriscontrol circuit 121 drives an iris driver 123 and an IG meter 122according to the input level of the video signal, thereby controllingthe iris 103 to make adjustment of the amount of light.

The AF signal processing circuit 109 receives a gate signal from an AFframe generating circuit 110 which generates a gate signal for gating apredetermined area of a picked-up image in accordance with vertical andhorizontal synchronizing signals supplied from a timing generator 111,and extracts only a high-frequency component of the video signalcontained in an AF frame and performs processing of the extractedhigh-frequency component.

An lens control microcomputer 112 has a memory 113 which stores an AFprogram for making adjustment of focus according to the strength of anAF evaluation signal, a memory 114 which stores a zoom control programfor maintaining the focusing lens 105 in an in-focus state while causingthe focusing lens 105 to trace a cam locus, a memory 115 which storeslens cam data to be referred to by the lens control microcomputer 112during the tracing of a cam locus, and a memory 116 which stores a motorcontrol program for driving the focusing lens 105 and the variator lens102 during AF or zooming. The lens control microcomputer 112 performscontrol of lens driving as well as AF frame control for varying adistance measuring area.

In addition, the lens control microcomputer 112 and a system controlmicrocomputer (hereinafter referred to as the system controller) 124communicate predetermined information to each other, such as informationrelative to a zoom switch unit 125 and an AF/MF (manual focusing) modeselecting switch 126, which information is read by the system controller124 through AID conversion or the like, andmagnification-varying-operation information such as a zooming directionand a focal length for zooming which is controlled by the lens controlmicrocomputer 112. (The zoom switch unit 125 is a zoom switch whichoutputs a voltage according to the rotating angle of an operatingmember, and variable-speed zooming is effected according to the outputvoltage.) A driver 118 outputs driving energy to a zooming motor 117 fordriving the variator lens 102, in accordance with an instruction todrive the variator lens 102, whereas a driver 120 outputs driving energyto a focusing motor 119 for driving the focus lens 105, in accordancewith an instruction to drive the focusing lens 105, both instructionsbeing outputted from the lens control microcomputer 112. The motors 117and 119 are provided for driving the variator lens 102 and the focusinglens 105, respectively.

A method of driving the lens driving motors 117 and 119 will bedescribed below. In the following description, by way of example, bothmotors 117 and 119 are assumed to be stepping motors.

The lens control microcomputer 112 determines a driving speed for thezooming motor 117 and a driving speed for the focusing motor 119 byprogram processing, and supplies the respective driving speeds to thedriver 118 for driving the zooming motor 117 and to the driver 120 fordriving the focusing motor 119, in the form of rotating-frequencysignals for the respective stepping motors 117 and 119. The lens controlmicrocomputer 112 also supplies drive/stop instructions for therespective motors 117 and 119 and rotating-direction instructions forthe respective motors 117 and 119 to the corresponding drivers 118 and120. The drive/stop signal and the rotating-direction signal for thezooming motor 117 primarily correspond to the state of the zoom switchunit 125, whereas those for the focusing motor 119 correspond to a driveinstruction which is determined by processing executed in the lenscontrol microcomputer 112 during AF or zooming.

Each of the motor drivers 118 and 120 sets the phase order of four motorexcitation phases to a phase order for forward rotation or a phase orderfor reverse rotation according to the corresponding rotating-directionsignal, and outputs voltages (or currents) for the respective four motorexcitation phases while varying the voltages (or the currents),according to the received rotating-frequency signal, thereby controllingthe rotating direction and rotating frequency of the corresponding oneof the motors 117 and 119. The respective motor drivers 118 and 120 turnon/off their outputs to the motors 117 and 119 according to thecorresponding drive/stop instructions.

FIG. 9 is a control flowchart for carrying out the first embodiment,which is processed in the lens control microcomputer 112 once during onevertical synchronizing period, and is a view showing detailed contentsto be executed in Step S5 of FIG. 7 described previously in connectionwith the related art. The operation of the first embodiment will bedescribed below with reference to FIGS. 9, 10, 11 and 12.

FIG. 12 shows a data table of the cam locus information of FIG. 3(described previously as the related art) which is stored in the lenscontrol microcomputer 112 for executing lens control. The data tableshows in-focus position data A(n, v) for the focusing lens 105 for eachsubject distance, and the in-focus position of the focusing lens 105varies according to the position of the variator lens 102 for eachsubject distance. The subject distance varies along the column of avariable n, and a zoom position (focal length) varies along the row of avariable v.

In this data table, n=0 represents the subject distance of a subjectlying at infinity, and as n becomes larger, the subject distance variestoward a closest distance, and n=m represents a subject distance of 1cm. Further, v=0 represents a zoom position for a wide-angle end, and asv becomes larger, the focal length increases, and v=s represents a zoomposition for a telephoto end. According to the data table, one cam locusis drawn with one column of table data.

The operation of the first embodiment will be described below withreference to the processing sequence shown in FIG. 9.

Step S31 is a routine for setting a driving speed Zsp of the zoomingmotor 117 so that the variator lens 102 can perform a naturalmagnification varying operation according to information indicative ofthe state of depression of the zoom switch unit 125, which informationis received by the lens control microcomputer 112 from the systemcontroller 124.

Step S32 is a routine for identifying the distance to a subject which isbeing photographed, on the basis of the current positions of thevariator lens 102 and the focusing lens 105, and storing informationindicative of the identified subject distance in a memory area (notshown) such as a RAM in the form of three locus parameters α, β and γ.This routine consists of the processing contents shown in FIG. 10 whichwill be described below. In the description of the first embodiment, itis assumed for the sake of simplicity that the focusing lens 105 ismaintaining an in-focus state at the current lens position.

Referring to FIG. 10, Step S51 executes the processing of calculatingwhich of the zoom areas v on the table of FIG. 12 corresponds to acurrent zoom position Zx, the zoom areas v being obtained by dividingthe entire zoom area from the wide-angle end to the telephoto end into sequal areas. The calculating method will be described below withreference to FIG. 11.

In Step S71 of FIG. 11, the zoom area (variable) v is cleared, and azoom position Z(v) at a boundary in the zoom area v is calculated inaccordance with the following equation (6), The zoom position Z(v)corresponds to any one of the positions Z0, Z1, Z2, . . . of thevariator lens 102 which are shown in FIG. 4 described previously:

Z(v)=(zoom position for telephoto end−zoom position for wide-angleend)×v/s+zoom position for wide-angle end.  (6)

In Step S73, it is determined whether the zoom position Z(v) obtained inStep S72 is equal to a current zoom position Zx. If the zoom positionZ(v) is equal to the zoom position Zx, it is determined that the zoomposition Zx lies on the boundary in the zoom area v, and a boundary flagis set to 1 in Step S77. If the answer in Step S73 is false, it isdetermined in Step S74 whether the zoom position Zx is smaller than thezoom position Z(v). If the answer in Step S74 is true, it is determinedthat the zoom position Zx lies between a zoom position Z(v−1) and thezoom position Z(v), and the boundary flag is set to 0 in Step S73. Ifthe answer in Step S74 is false, the zoom area (variable) v isincremented, and the process returns to Step S72.

When the above-described processing is repeatedly performed and theprocessing shown in FIG. 11 is completed, it can be determined whetherthe current zoom position Zx is present in the k-th zoom area v on thetable shown in FIG. 12 and is present at a boundary in the k-th zoomarea v.

Referring again to FIG. 10, since the zoom area v is determined in StepS51, it is calculated in the following processing where the position ofthe focusing lens 105 (a focus position) is on the table shown in FIG.12.

First, in Step S52, the subject distance variable n is cleared, and itis determined in Step S53 whether the current zoom position Zx ispresent at a boundary in the k-th zoom area v. If the value of theboundary flag is 0, it is determined that the current zoom position Zxdoes not lie on the boundary, and the process proceeds to Step S55. InStep S55, Zk←Z(v) and Zk−1←Z(v−1) are set.

Then, in Step S56, four table data A(n, v−1), A(n, v), A(n+1, v−1) andA(n+1, v) are read, and ax and bx are calculated from the respectiveequations (2) and (3) described above.

On the other hand, if the answer in Step S53 is true, the in-focus focuspositions A(n, v) and A(n+1, v) for the subject distance n and the zoomposition v are read and memorized as ax and bx, respectively.

In Step S58, it is determined whether a current focus position Px is notless than ax. If the answer in Step S58 is true, it is determined inStep S59 whether the current focus position Px is not less than bx. Ifthe answer is false, it is determined that the current focus position Pxlies between the subject distances n and n+1, and the locus parametersα, β and γ obtained at this time are stored in the memory area in StepsS63, S64 and S65, respectively.

In Step S63, the locus parameter α is set to a α=Px−ax, then, in StepS64, the locus parameter β is set to β=bx−ax, and then, in Step S65, thelocus parameter γ is set to γ=n. If the answer in Step S58 is false, itis determined that the current focus position Px is at ultra infinity,and the process proceeds to Step S62 in which the locus parameter α isset to α=0. Then, in Step S64, a locus parameter for infinity is storedin the memory area.

If the answer in Step S59 is true, it is determined that the currentfocus position Px is closer to the closest-distance end, and the subjectdistance n is incremented in Step S60, and it is determined in Step S61whether the subject distance n is not greater than a closest subjectdistance m. If the answer is true, the process returns to Step S53. Ifthe answer in Step S61 is false, it is determined that the current focusposition Px is at the ultra closest distance, and the process proceedsto Step S62 in which the locus parameters α, β and γ for the closestdistance are stored in the memory area.

Referring again to FIG. 9, in Step S32, it is calculated where thecurrent zoom position Zx and the current focus position Px are locatedin the cam locus diagram shown in FIG. 3, and the locus parameters α, βand γ are recorded. Step S33 is a routine for calculating a zoomposition Zx′ to be reached by the variator lens 102 after one verticalsynchronizing period. Letting Zsp (pps) be the zoom driving speed of thezooming motor 117 (a zooming speed), the zoom position Zx′ to be reachedby the variator lens 102 after one vertical synchronizing period isgiven by the following equation (7). The unit “pps” represents therotating speed of a stepping motor, and indicates the number of stepsper second of the stepping motor during rotation (1 step=1 pulse). Thesign “±” used in Equation (7) indicates different moving directions ofthe variator lens 102, and the sign “+” indicates that the variator lens102 moves toward the telephoto end, while the sign “−” indicates thatthe variator lens 102 moves toward the wide-angle end:

Zx′=Zx±Zsp/(vertical synchronizing frequency).  (7)

Then, in Step S34, it is determined in which zoom area v′ the zoomposition Zx′ is present. Step S34 is a processing similar to that shownin FIG. 11, and Zx→Zx′ and v→v′ are set in a manner similar to thatshown in FIG. 11.

Then, in Step S35, it is determined whether the zoom position Zx′ after1V (one vertical synchronizing period) is present at a boundary in thezoom area v′. If the value of the boundary flag is 0, it is determinedthat the zoom position Zx′ does not lie on a boundary, and the processproceeds to Step S36. In Step S36, Zk←Z(v′) and Zk−1←Z(v′−1) are set.

Then, in Step S37, four table data A(γ, v′−1), A(γ, v′), A(γ+1, v′−1)and A(γ+1, v′) for the subject distance γ identified by the processingshown in FIG. 10 are read, and in Step S38, ax′ and bx′ are calculatedfrom the respective equations (2) and (3) described above.

On the other hand, if the answer in Step S35 is true, the processproceeds to Step S39, in which the in-focus focus positions A(γ, v′) andA(γ+1, v′) for the subject distance γ and the zoom area v′ are read andmemorized as ax′ and bx′, respectively. Then, in Step S40, an in-focusfocus position Px′ to be reached by the focusing lens 105 when thevariator lens 102 reaches the zoom position Zx′ is calculated. A targettrace position after 1V is expressed by the following equation (8) byusing Equation (1):

Px′=(bx′−ax′)×α/β+ax′.  (8)

The difference between the target trace position and the current focusposition becomes:

ΔF=(bx′−ax′)×α/β+ax′−Px.  (9)

Then, in Step S41, a focusing standard moving speed Vf0 is calculated.Vf0 is obtained by dividing a focus position difference ΔF by the timerequired for the variator lens 102 to move the distance of ΔF. When theprocessing shown in FIG. 9 is completed, the process proceeds to Step S7of FIG. 7 (described previously). In Step S7, if zooming is beingexecuted, the focusing lens 105 is moved for focus compensation at thefocusing speed determined in Step S40 in the direction indicated by thesign of the focusing speed (toward the closest-distance end in the caseof the positive sign or toward the infinity end in the case of thenegative sign).

As described above, by predicting a destination to be reached by thevariator lens 102 after one vertical synchronizing period anddetermining a trace destination on a cam locus to be reached by thefocusing lens 105 according to the position of the destination of thevariator lens 102, it is possible to realize manual-mode zoomingperformance which is capable of stably maintaining an in-focus stateirrespective of the zooming speed without performing a plurality ofcam-locus tracing computations for one vertical synchronizing period.Accordingly, it is possible to reduce the load on the microcomputer. Inaddition, in calculating the focusing standard moving speed Vf0, thetime required for the variator lens 102 to move by the distance of thefocus position difference ΔF is the time of a vertical synchronizingperiod, so that even if Vf0 is calculated by a division computation, acomputational error is small and a cam locus can be accurately traced.

Second Embodiment

In the description of the first embodiment, reference has been made tothe tracing method of accurately tracing a cam locus while reducing theload on a microcomputer. Even during a manual mode in which an in-focuscam locus to be traced is previously identified or even during an AFmode, as long as zooming is effected from a telephoto side toward awide-angle side, the tracing method of the first embodiment does notgive rise to defocusing. However, during zooming from the wide-angleside toward the telephoto side in the AF mode, since the variator lensmoves in the direction in which in-focus cam loci gradually diverge froma point of convergence as described previously, defocusing will occur ifa zooming operation is not performed while an in-focus cam locus isbeing identified. To solve the above problem, in accordance with thesecond embodiment which will be described below, there is provided anextended version of the first embodiment which can prevent occurrence ofdefocusing even during zooming from the wide-angle side toward thetelephoto side in the AF mode in the tracing method of the firstembodiment.

FIG. 13 is a flowchart similar to FIG. 9, showing the details of Step S5shown in FIG. 7. The processing shown in FIG. 13 handles a method ofcausing the focusing lens 105 to trace a cam locus while making a zigzagmovement to identify the cam locus to be traced as described previously.Incidentally, since the processing routine from Step S31 to Step S41 ispreviously described with reference to FIG. 9, the detailed descriptionof the same processing routine is omitted.

In Step S81 which executes the processing of initializing eachparameter, an inversion flag to be used in subsequent steps is cleared.Step S82 is a routine for calculating correction speeds Vf⁺ and Vf⁻ forzigzag movement from the focusing standard moving speed Vf0 obtained inStep S41. In Step S82, an amount-of-correction parameter 8 and thecorrection speeds Vf⁺ and Vf⁻ are calculated in the following manner.

FIG. 14 is a view aiding in describing a method of calculating thecorrection speeds Vf⁺ and Vf⁻ according to the amount-of-correctionparameter δ. In FIG. 14, the horizontal axis represents the position ofthe variator lens 102, while the vertical axis represents the positionof the focusing lens 105, and a curve 604 represents a cam locus to betraced.

The focusing speed at which the position of the focusing lens 105 variesby an amount y as the position of the variator lens 102 varies by anamount x is the standard speed Vf0 calculated with a direction vector1403, while the focusing speed at which the position of the focusinglens 105 varies by an amount n or m with respect to the displacement yas the position of the variator lens 102 varies by the amount x is thecorrection speed Vf⁺ or Vf⁻ to be obtained.

The amounts n and m are determined so that a direction vector 1401 of aspeed at which to drive the focusing lens 105 toward a closest-distanceside from the displacement y (the sum of the standard speed Vf0 and thepositive correction speed Vf⁺) and a direction vector 1402 of a speed atwhich to drive the focusing lens 105 toward an infinity side from thedisplacement y (the sum of the standard speed Vf0 and the negativecorrection speed Vf⁻) are spaced apart from each other in such a mannerthat each of the direction vectors 1401 and 1402 makes an equal angle δwith the direction vector 1403.

First, n and m are obtained. From FIG. 14, geologically,

tan θ=y/x, tan(θ−δ)=(y−m)/x, tan(θ+δ)=(y+n)/x,  (10)

and also

tan(θ±δ)=(tan θ±tan δ)/(1±(−1)×tan θ×tan δ).  (11)

From (10) and (11),

m=(x2+y2)/(x/k+y),  (12)

n=(x2+y2)/(x/k−y), where tan δ=k.  (13)

Thus, n and m are obtained. The correction angle δ is a variable usingparameters such as depth of field and focal length. In this manner, theincrease-decrease period of a sharpness signal level which variesaccording to the driven state of the focusing lens 105 can be keptconstant with respect to a predetermined amount of variation in theposition of the focusing lens 105, whereby it is possible to reduce thepossibility of missing a cam locus to be traced during zooming.

According to the value of δ, the value of k is stored in the memory areaof the lens control microcomputer 112 in the form of a data table, and aparticular value of k is read from the stored values, as required, tocalculate Equations (12) and (13). If it is assumed here that theposition of the variator lens 102 varies by x per unit time, then thezooming speed Zsp=x, the focusing standard moving speed Vf0=y, thecorrection speed Vf⁺=n, and the correction speed Vf⁻=m, and thecorrection speeds Vf⁺ and Vf⁻ (negative speed) can be obtained fromEquations (12) and (13).

Referring again to FIG. 13, in the processing of Step S83, it isdetermined whether zooming is being executed, on the basis ofinformation indicative of the state of operation of the zoom switch unit125, which information is obtained from a mutual communication with thesystem controller 124 in Step S3 of FIG. 7. If the answer in Step S83 istrue, the process proceeds to Step S86. If the answer is false, theprocess proceeds to Step S84, in which a value TH1 is obtained bysubtracting an arbitrary constant μ from the current value of an AFevaluation signal level, thereby determining an AF evaluation signallevel which becomes a criterion for switchover betweencorrecting-direction vectors (a criterion for switchover in zigzagmovement), as described previously with reference to FIGS. 6(A) and6(B). This value TH1 is determined immediately before the start ofzooming, and corresponds to the level of the minimum value 602 shown inFIG. 6(A).

Then, in Step S85, a correction flag is cleared, and the processingshown in FIG. 13 is completed. The correction flag is a flag whichindicates whether the tracing of a cam locus is in a state corrected ina positive direction (the value of the correction flag=1) or in a statecorrected in a negative direction (the value of the correction flag=0).

If it is determined in Step S83 that zooming is being executed, it isdetermined in Step S86 whether zooming from the wide-angle side towardthe telephoto side is being executed. If the answer is false, theprocess proceeds to Step S89 in which Vf⁺=0 and Vf⁻=0 are set, and thenproceeds to Step S90. If the answer in Step S86 is true, it isdetermined in Step S87 whether the current AF evaluation signal level issmaller than TH1. If the answer is false, the process proceeds to StepS90. If the answer is true, since the current AF evaluation signal levelis lower than the level of TH1 (the minimum value 602) shown in FIG.6(A), the process proceeds to Step S88, in which the inversion flag isset to 1 which means an instruction to execute a switchover between thecorrecting directions.

In Step S90, it is determined whether the value of the inversion flagis 1. If the answer is true, it is determined in Step S91 whether thecorrection flag is set to 1. If the answer in Step S91 is false, theprocess proceeds to Step S94, in which the correction flag is set to 1(the state corrected in the positive direction) and a focusing speed Vfis determined from Equation (4) as follows:

 Vf=Vf 0+Vf ⁺ (where Vf ⁺≧0).  (14)

If the answer in Step S91 is true, the process proceeds to Step S93, inwhich the correction flag is reset to 0 (the state corrected in thenegative direction) and the focusing speed Vf is determined fromEquation (5) as follows:

Vf=Vf 0+Vf ⁻ (where Vf ⁻≦0).  (15)

If the answer in Step S90 is false, it is determined in Step S92 whetherthe correction flag is set to 1. If the answer is true, the processproceeds to Step S94, whereas if the answer is false, the processproceeds to Step S93.

After the completion of the processing shown in 13, the drivingdirection and the driving speed of each of the focusing lens 105 and thevariator lens 102 are selected according to the mode of operation inStep S6 of FIG. 7. In the case of a zooming operation, in Step S6, thedriving direction of the focusing lens 105 is set so that the focusinglens 105 is driven toward the closest-distance end or the infinity endaccording to whether the focusing speed Vf obtained in Step S93 or S94is positive or negative.

As described above, according to the second embodiment, the method ofpredicting a destination to be reached by the variator lens 102 afterone vertical synchronizing period and determining a trace destination ona cam locus to be reached by the focusing lens 105 according to theposition of the destination of the variator lens 102 can also be appliedto zooming from the wide-angle side to the telephoto side during AF.Accordingly, it is possible to realize comfortable zooming performancefor AF which is capable of stably maintaining an in-focus stateirrespective of the zooming speed while reducing the load on themicrocomputer.

Third Embodiment

Although each of the above-described first and second embodiments uses astepping motor as an actuator for driving a focusing lens, a thirdembodiment which will be described below uses a linear motor whichfeatures low drive noise, small drive vibration and superior high-speeddriving performance.

First of all, the merit of using such linear motor as the focusing motor119 for driving the focusing lens 105 (refer to FIG. 1) will bedescribed. In a camera provided with an inner focus type of lens, if itsfocusing lens needs to keep maintaining an in-focus state while itsvariator lens is being moved at a uniform speed, it is necessary toincrease the moving speed of the focusing lens near the telephoto end atwhich the slope of a cam locus becomes sharp. However, if a steppingmotor is used as a focusing motor in the camera, the speed of thestepping motor which is required for increasing the moving speed of thefocusing lens near the telephoto end may exceed a controllable limitspeed.

To prevent the required speed of the stepping motor from exceeding thecontrollable limit speed, it is general practice to adopt a method ofmaintaining an in-focus state by reducing the speed of a zooming motorwhile maintaining the speed of the focusing motor within thecontrollable limit speed.

However, if a linear motor which is superior in high-speed drivingperformance is used as the focusing-lens driving motor, not only is itunnecessary to reduce the speed of the zooming motor, but it is alsopossible to increase the speed of the variator lens which moves at auniform speed. Accordingly, it is possible to realize high-speedzooming.

FIGS. 16(A) and 16(B) show an example of a lens moving mechanism towhich a moving coil type of voice coil motor is applied as such linearmotor. FIG. 16(B) is a vertical sectional view taken along line B—B ofFIG. 16(A). As shown in FIGS. 16(A) and 16(B), a yoke 1617 a and a coil1616 which is wound around a bobbin 1619 are disposed around theperiphery of a lens holding frame 1611 which holds lenses 1610 b 1 to1601 b 3, and a yoke 1617 b and a magnet 1615 bonded thereto aredisposed outside the coil 1616. The yokes 1617 a and 1617 b and themagnet 1615 are secured to a fixed tube 1602. The lens holding frame1611 is held for movement along an optical axis 1605 by two guide rods1603 a and 1603 b parallel to the optical axis 1605. Since the magnet1615 is magnetized as shown in FIG. 16(B), a radial magnetic field isformed between the yokes 1617 a and 1617 b. The coil 1616 is presentbetween the yokes 1617 a and 1617 b and is wound in the circumferentialdirection of the bobbin 1619. Accordingly, if a current is made to flowthrough the coil 1616, a driving force acting along the optical axis isproduced so that the lens holding frame 1611 which is formed integrallywith the bobbin 1619 and the lenses 1610 b 1 to 1601 b 3 are driven tomove along the optical axis.

FIG. 15 is a block diagram of an image pickup apparatus in which thelinear motor having the arrangement and construction shown in FIGS.16(A) and 16(B) is used as a focusing-lens driving motor. In FIG. 15,identical reference numerals are used to denote constituent elementssimilar to those shown in FIG. 1, and the description thereof is omittedherein.

A method of controlling the linear motor will be described below withreference to FIG. 15. The position of the focusing lens 105 is detectedby a position encoder 1502, and the output signal of the positionencoder 1502 is inputted to and appropriately gain-controlled by anamplifying circuit 1503. The output signal of the amplifying circuit1503 is inputted to a comparing circuit 1504. In the meantime, a targetsignal for moving the focusing lens 105 is outputted from the lenscontrol microcomputer 112 to the comparing circuit 1504.

The comparing circuit 1504 outputs a deviation signal equivalent to thedifference between the two signals to an integrating circuit 1505, andthe integrating circuit 1505 performs integration of the deviationsignal and supplies the integral output signal to an adding circuit1507. The output signal of the position encoder 1502 is also inputted toa differentiating circuit 1506, and the differentiating circuit 1506performs differentiation of the input signal and supplied thedifferential output signal to the adding circuit 1507. The addingcircuit 1507 adds together the integral output signal and thedifferential output signal, and sends the sum signal to a motor driver1508 so that the motor driver 1508 applies a voltage to a motor coil1501 to perform loop control. A reference voltage is applied to one endof the motor coil 1501, and the motor driver 1508 applies to the otherend of the motor coil 1501 a voltage which is positive or negative withrespect to the reference voltage, thereby switching the polarity of thecurrent flowing through the motor coil 1501 to change the movingdirection of the focusing lens 105. In addition, the motor driver 1508varies its output voltage level to vary the amount of driving of thefocusing lens 105.

The speed feedback given by the differentiating circuit 1506 is intendedto stabilize the entire loop system and to inhibit an abrupt movement ofthe focusing lens 105 so that a natural picked-up image is produced aswell as so that the focusing lens 105 can be prevented from movingbeyond its movable range and colliding with a mechanical member. Thelens control microcomputer 112 generates a movement target signal byreferring to a data table for a desired lens position and converting thecorresponding data into an output value. The data table contains, forexample, a predetermined correlation between the output level of thetarget signal and the position of the focusing lens 105, and ispreviously stored in the lens control microcomputer 112.

A method of tracing a cam locus according to the third embodiment willbe described below with reference to FIG. 17. FIG. 17 is a flowchartshowing in detail the zooming processing routine of Step S5 shown inFIG. 7. Incidentally, in the case of focusing control using a linearmotor, the processing for the focusing motor shown in FIG. 7 does notneed the item “speed”, and adopts the above-described type of controlmethod of outputting a target position signal. In the processing routineshown in FIG. 17, identical step numbers are used to denote processingsteps similar to those shown in FIGS. 9 and 13.

Step S31 of FIG. 17 is a routine for setting the driving speed Zsp ofthe zooming motor 117 so that the variator lens 102 can perform anatural magnification varying operation according to informationindicative of the state of depression of the zoom switch unit 125, whichinformation is received by the lens control microcomputer 112 from thesystem controller 124.

Step S32 is a routine for identifying the distance to a subject which isbeing photographed, on the basis of the current positions of thevariator lens 102 and the focusing lens 105, and storing informationindicative of the identified subject distance in the memory area such asa RAM in the form of three locus parameters α, β and γ. This routineconsists of the processing contents shown in FIG. 10 as describedpreviously in connection with the first embodiment. In Step S32, it iscalculated where the current positions of the variator lens 102 and thefocusing lens 105 are located in the cam locus diagram shown in FIG. 3,and the locus parameters α, β and γ are stored.

Step S33 is a routine for calculating a zoom position Zx′ to be reachedby the variator lens 102 after one vertical synchronizing period.Letting Zsp (pps) be the zooming speed determined in Step S33, the zoomposition Zx′ to be reached by the variator lens 102 after one verticalsynchronizing period is given by the above-described equation (7).

Then, in Step S34, it is determined in which zoom area v′ the zoomposition Zx′ is present. Step S34 is a processing similar to that shownin FIG. 11, and Zx→Zx′ and v→v′ are set in a manner similar to thatshown in FIG. 11.

Then, in Step S35, it is determined whether the zoom position Zx′ after1V (one vertical synchronizing period) is present at a boundary in thezoom area v′. If the value of the boundary flag is 0, it is determinedthat the zoom position Zx′ does not lie on a boundary, and the processproceeds to Step S36.

In Step S36, Zk←Z(v′) and Zk−1←Z(v′−1) are set. Then, in Step S37, fourtable data A(γ, v′−1), A(γ, v′), A(γ+1, v′−1) and A(γ+1, v′) for thesubject distance γ identified by the processing shown in FIG. 10 areread, and in Step S38, ax′ and bx′ are calculated from the respectiveequations (2) and (3) described above.

On the other hand, if the answer in Step S35 is true, the processproceeds to Step S39, in which the in-focus focus positions A(γ, v′) andA(γ+1, v′) for the subject distance γ and the zoom area v′ are read andmemorized as ax′ and bx′, respectively. Then, in Step S40, an in-focusfocus position Px′ to be reached by the focusing lens 105 when thevariator lens 102 reaches the zoom position Zx′ is calculated. Astandard target trace position to be reached the focusing lens 105 after1V is given from the above-described equation (8) as follows:

Px′=(bx′−ax′)×α/β+ax′.  (16)

In Step S81, an inversion flag to be used in subsequent steps iscleared. In Step S101, correction positions Pf⁺ and Pf⁻ for zigzagmovement are calculated on the basis of the focusing standard targetposition Px′ obtained in Step S40 so that the linear motor can be usedto realize a zooming operation similar to that of the aforesaid steppingmotor in the AF mode.

As described above with reference to FIG. 14, the correction speeds Vf⁺and Vf⁻ for zigzag movement are determined as variation speeds relativeto the standard moving speed Vf0 according to the amount-of-correctionparameter δ. Since each of the correction speeds Vf⁺ and Vf⁻ representsthe amount of movement per unit time of the focusing lens 105, theamount of correction movement based on the standard target position Px′for one vertical synchronizing period becomes an amount obtained bydividing the absolute value of each of the correction speeds Vf⁺ and Vf⁻by a vertical synchronizing period. Accordingly,

Pf ⁺ =|Vf ⁺|/(vertical synchronizing period),  (17)

 and

Pf ⁻ =|Vf ⁻|/(vertical synchronizing period).  (18)

Then, in the processing of Step S83, it is determined whether zooming isbeing executed, on the basis of information indicative of the state ofoperation of the zoom switch unit 125, which information is obtainedfrom a mutual communication with the system controller 124 in Step S3 ofFIG. 7. If the answer in Step S83 is true, the process proceeds to StepS86. If the answer is false, the process proceeds to Step S84, in whicha value TH1 is obtained by subtracting an arbitrary constant μ from thecurrent value of an AF evaluation signal level, thereby determining anAF evaluation signal level which becomes a criterion for switchoverbetween correcting-direction vectors (a criterion for switchover inzigzag movement), as described previously with reference to FIGS. 6(A)and 6(B). This value TH1 is determined immediately before the start ofzooming, and corresponds to the level of the minimum value 602 shown inFIG. 6(A).

Then, in Step S85, a correction flag is cleared, and the processingshown in FIG. 17 is completed. The correction flag is a flag whichindicates whether the tracing of a cam locus is in a state corrected ina positive direction (the value of the correction flag=1) or in a statecorrected in a negative direction (the value of the correction flag=0).

If it is determined in Step S83 that zooming is being executed, it isdetermined in Step S86 whether zooming from the wide-angle side towardthe telephoto side is being executed. If the answer is false, theprocess proceeds to Step S102 in which Pf⁺=0 and Pf⁻=0 are set, and thenproceeds to Step S90. If the answer in Step S86 is true, it isdetermined in Step S87 whether the current AF evaluation signal level issmaller than TH1. If the answer is false, the process proceeds to StepS90. If the answer is true, since the current AF evaluation signal levelis lower than the level of TH1 (the minimum value 602) shown in FIG.6(A), the process proceeds to Step S88, in which the inversion flag isset to 1 which means an instruction to execute a switchover between thecorrecting directions.

In Step S90, it is determined whether the value of the inversion flagis 1. If the answer is true, it is determined in Step S91 whether thecorrection flag is set to 1. If the answer in Step S91 is false, theprocess proceeds to Step S104, in which the correction flag is set to 1(the state corrected in the positive direction) and a focusing targetvalue Pf to be reached by the focusing lens 105 after one verticalsynchronizing period is determined as follows:

Pf=Px′+Pf ⁺.  (19)

If the answer in Step S91 is true, the process proceeds to Step S103, inwhich the correction flag is reset to 0 (the state corrected in thenegative direction) and the focusing target value Pf to be reached bythe focusing lens 105 after one vertical synchronizing period isdetermined as follows:

Pf=Px′−Pf ⁻.  (20)

If the answer in Step S90 is false, it is determined in Step S92 whetherthe correction flag is set to 1. If the answer is true, the processproceeds to Step S104, whereas if the answer is false, the processproceeds to Step S103 and the processing shown in FIG. 17 is completed.

As is apparent from the above description, according to the thirdembodiment, the method of predicting a destination to be reached by thevariator lens 102 after one vertical synchronizing period anddetermining a trace destination on a cam locus to be reached by thefocusing lens 105 according to the position of the destination of thevariator lens 102 can also be applied to focus-position control using alinear motor. Accordingly, it is possible to realize high-speed zoomingwhile preventing the problem that, for example, when the variator lens102 moves from the position Z4 to the position Z6 (as viewed in FIG. 4)within the time of one vertical synchronizing period, only the positionof the focusing lens 105 is left at the point p5 (p6″ in FIG. 4) anddefocusing is caused.

In particular, even if computation timing and the zooming speed vary,the time required for the variator lens 102 to move for a predeterminedperiod of time (one vertical synchronizing period in each of the firstto third embodiments) is constant, so that if only the time required forthe variator lens 102 to moved by the difference in distance between acalculated trace target position and the current focus position isfound, it is possible to readily shift the focus position to a targetposition according to a position to be reached by the variator lens 102after the predetermined period of time. Accordingly, it is possible toprovide a comfortable image pickup apparatus having both superiorfocusing performance and high-speed zooming performance.

As is also apparent from the above description, according to each of thefirst to third embodiments, it is possible to provide an image pickupapparatus and an image pickup method both of which make it possible toinexpensively realize comfortable and superior zooming performancewithout the need to produce loads on a processing microcomputer andirrespective of the zooming speed of a magnification varying operationand the kind of focusing motor.

Specifically, by predicting a destination to be reached by the variatorlens 102 after the predetermined period of time and determining a tracedestination on a cam locus to be reached by the focusing lens 105according to the position of the destination of the variator lens 102,it is possible to realize manual-mode zooming performance which iscapable of stably maintaining an in-focus state irrespective of thezooming speed without performing a plurality of cam-locus tracingcomputations within the predetermined period of time. Accordingly, it ispossible to reduce the load on the microcomputer. In addition, since itis possible to reduce a computational error in calculating the focusingstandard moving speed Vf0, it is possible to accurately trace a camlocus.

In addition, the method of predicting a destination to be reached by thevariator lens 102 after the predetermined period of time and determininga trace destination on a cam locus to be reached by the focusing lens105 according to the position of the destination of the variator lens102 can also be applied to zooming during AF. Accordingly, it ispossible to realize comfortable zooming performance for AF which iscapable of stably maintaining an in-focus state irrespective of thezooming speed while reducing the load on the microcomputer.

In addition, the method of predicting a destination to be reached by thevariator lens 102 after the predetermined period of time and determininga trace destination on a cam locus to be reached by the focusing lens105 according to the position of the destination of the variator lens102 can also be applied to focus-position control using a linear motor.Accordingly, it is possible to realize ultra-high-speed zooming whilepreventing a problem peculiar to a system placed under loop positioncontrol, i.e., the problem that even if the zoom position changes, onlythe focus position does not change and defocusing is caused. Inparticular, even if the computation timing and the zooming speed vary,the time required for the variator lens 102 to move for a predeterminedperiod of time is constant, so that if only the time required for thevariator lens 102 to moved by the difference in distance between acalculated trace target position and the current focus position isfound, it is possible to readily shift the focus position to a targetposition according to a position to be reached by the variator lens 102after the predetermined period of time. Accordingly, it is possible toprovide a comfortable image pickup apparatus having both superiorfocusing performance and high-speed zooming performance.

In addition, the method of predicting a destination to be reached by thevariator lens 102 after the predetermined period of time and determininga trace destination on a cam locus to be reached by the focusing lens105 according to the position of the destination of the variator lens102 can also be applied to both focus position control using a linearmotor and zooming during AF. Accordingly, it is possible to realizecomfortable zooming performance for AF which is capable of stablymaintaining an in-focus state irrespective of the zooming speed.

In addition, since the aforesaid predetermined period of time is onevertical synchronizing period, it is possible to synchronize thepredetermined period of time with the timing of generating a focusvoltage signal from an picked-up image signal. Accordingly, only ifzooming control processing is executed once for one verticalsynchronizing period, it is possible to identify an in-focus cam locusand realize zooming performance free of defocusing.

Fourth Embodiment

A fourth embodiment of the present invention will be described below.The fourth embodiment is intended to enable accurate position controland speed control by using an inner focus type of lens and by using alinear motor (or a voice coil motor) as an actuator. The fourthembodiment will be described below in detail along with the backgroundthereof.

An image pickup apparatus such as a video camera having atwo-dimensional image pickup element or the like has heretofore adopteda focusing method which includes detecting the sharpness of an imagedisplayed on the basis of a video signal obtained by picking up an imageof a subject, and controlling the position of a focusing lens so thatthe sharpness detected becomes a maximum.

To evaluate the sharpness, it is general practice to use the strength ofa high-frequency component of a video signal extracted by a band-passfilter or the detection strength of a defocusing width of a video signalextracted by a differentiating circuit or the like. In a case where animage of a subject is picked up, if the focusing lens is out of focus,the strength of such high-frequency component and the detection strengthof such defocusing width are small, but as the focusing lens approachesan in-focus point, the level of such strength signal becomes larger. Ifthe focusing lens completely reaches the in-focus point, the level ofthe strength signal reaches a maximum.

Accordingly, during position control, if the degree of such sharpness issmall, the focusing lens is moved as fast as possible in the directionin which the degree of the sharpness becomes greater, and as the degreeof the sharpness becomes greater, the focusing lens is moved slower.When the degree of the sharpness reaches the maximum value, the focusinglens is precisely stopped on “the top of a hill”, i.e., brought intofocus.

Such a focus adjusting method (autofocus system) using theabove-described position control of the focusing lens is generallycalled a hill-climbing autofocus system (hereinafter referred to as“hill-climbing AF”). The hill-climbing AF system has recently becomepopular in latest video cameras which are reduced in size and weight,because the hill-climbing AF system makes it possible to realize anautofocus (AF) mechanism by using a simple system.

As described previously, to realize further reductions in the size andweight of a video camera or the like, it has also become popular to usean inner focus type of lens system, such as that shown in FIG. 2, as alens system for the video camera or the like.

In the inner focus type of lens system in which a focusing lens isdriven to correct a variation in a focal plane during zooming, since thefocusing lens has a light weight, an actuator for driving the focusinglens can be reduced in size and weight and the focusing lens can bedriven at high speeds. In addition, it is possible to make a closestfocusing distance to a subject far smaller in optical terms.

A cam locus tracing method for the inner focus type of lens system is asdescribed previously with reference to FIGS. 2 to 5 and Equations (1) to(3), and the processing of control of the zooming operation of the innerfocus type of lens system is normally performed in synchronism with avertical synchronizing signal peculiar to a video camera.

However, in the case of a recent type of video camera having a farfaster zooming speed, for example, the variator lens 102 may often movefrom the position Z4 to the position Z6 (shown in FIG. 4) within thetime of one vertical synchronizing period.

During this time, if lens control is performed in synchronism with avertical synchronizing signal, the standard moving speed of the focusinglens 105 remains the speed at which the focusing lens 105 is moving fromp4 to p5, and the updating of the standard moving speed is not performeduntil the variator lens 102 reaches the position Z6. Accordingly, whenthe position of the variator lens 102 is Z6, the focusing lens 105 liesat a point p6′ on a line which rectilinearly extends from the line p4-p5in FIG. 4, so that defocusing occurs by the difference between p6 andp6′ and accurate tracing of a cam locus cannot be performed duringzooming.

To solve the above-described problem, it is considered to adopt acontrol system which predicts a position to be reached by the variatorlens 102 after one vertical synchronizing period, calculates acorrection position of the focusing lens 105 for making a correction ona focal plane with respect to the predicted position, and performs lenscontrol so that the focusing lens 105 reaches the correction positionafter one vertical synchronizing period.

In this control system, for example, a linear motor which features lowdrive noise, small drive vibration and superior high-speed drivingperformance is used in place of the above-described stepping motor as anactuator for driving the focusing lens 105.

First of all, the merit of using the aforesaid linear motor as theactuator for driving the focusing lens 105 will be described. In acamera or the like which is provided with an inner focus type of lenssystem 100 such as that shown in FIG. 2, if the focusing lens 105 needsto keep maintaining an in-focus state while the variator lens 102 isbeing moved at a uniform speed, it is necessary to increase the movingspeed of the focusing lens 105 near the telephoto end at which the slopeof a cam locus becomes sharp. However, if a stepping motor is used asthe aforesaid actuator, the speed of the stepping motor which isrequired for increasing the moving speed of the focusing lens 105 nearthe telephoto end may exceed a controllable limit speed.

To prevent the required speed of the stepping motor from exceeding thecontrollable limit speed, it is general practice to adopt a method ofmaintaining an in-focus state by reducing the driving speed of a motorfor moving the variator lens 102 while maintaining the speed of thestepping motor within the controllable limit speed.

However, if a linear motor which is superior in high-speed drivingperformance is used as the aforesaid actuator, not only is itunnecessary to reduce the driving speed of the motor for moving thevariator lens 102, but it is also possible to increase the speed of thevariator lens 102 which moves at a uniform speed. Accordingly, it ispossible to realize ultra-high-speed zooming.

If a stepping motor or a DC motor is used as the actuator for drivingthe focusing lens 105, it is necessary to use a driving-powertransmitting mechanism for converting the rotational driving force ofthe motor into a driving force for rectilinear movement for the purposeof lens driving, and the size and weight of the entire lens movingmechanism are, therefore, difficult to reduce In contrast, if the linearmotor is used, the driving-power transmitting mechanism is not neededand the size and weight of the entire lens moving mechanism can bereduced.

A lens moving mechanism to which, for example, a moving coil type ofvoice coil motor is applied as the above-described linear motor is asshown in FIGS. 16(A) and 16(B) referred to previously, and thedescription thereof is omitted.

An image pickup apparatus in which such lens moving mechanism is usedfor driving the focusing lens 105 shown in FIG. 2 has, for example, theconstruction shown in FIG. 30.

Light (image light) from a subject (not shown) passes through the firstlens group 101, the variator lens 102, the iris 103, the third lensgroup 104 and the focusing lens 105 in that order, and is focused on theimage pickup surface of the image pickup element 106 of an image pickupelement.

The image light focused on the image pickup surface of the image pickupelement 106 is converted into a video signal by photoelectricconversion. The video signal is amplified to an optimum signal level byan amplifier 807, and the amplified video signal is inputted to a camerasignal processing circuit 808.

The camera signal processing circuit 808 performs predetermined signalprocessing on the video signal supplied from the amplifier 807, andgenerates and outputs a standard television signal.

The video signal amplified by the amplifier 807 is also supplied to anAF signal processing circuit 809.

At this time, an AF frame generating circuit 810 generates a gate signalfor gating a predetermined area of an image picked up on the imagepickup surface of the image pickup element 106, in response to verticaland horizontal synchronizing signals supplied from a timing generator811 in accordance with AF-frame control (to be described later) providedby an AF microcomputer 812, and outputs the gate signal to the AF signalprocessing circuit 809.

The AF signal processing circuit 809 extracts only a high-frequencycomponent of the video signal contained in an AF frame from the videosignal supplied from the amplifier 807, in response to the gate signalsupplied from the AF frame generating circuit 810, and performspredetermined processing such as the processing of generating theabove-described AF evaluation signal.

The AF microcomputer 812 is arranged to perform processing for lenscontrol, such as focus adjustment according to the strength of the AFevaluation signal generated by the AF signal processing circuit 809,zooming control for maintaining the focusing lens 105 in an in-focusstate while causing it to trace a cam locus, lens driving control suchas motor control for driving the focusing lens 105 and the variator lens102 during AF or zooming, and AF frame control for varying a distancemeasuring area.

In addition, the AF microcomputer 812 sends an instruction to drive thevariator lens 102 to a zooming motor driver 814, in accordance with aswitch state supplied from a zoom switch 823, thereby causing thezooming motor driver 814 to drive a zooming motor 813.

If the zooming motor 813 is the above-described type of stepping motor,the AF microcomputer 812 determines a driving speed of the zooming motor813 on the basis of its built-in processing program, and supplies thedriving speed to the zooming motor driver 814 for driving the zoomingmotor 813, as a rotating-frequency signal.

The AF microcomputer 812 also supplies a drive/stop instruction and arotating-direction instruction signal for the zooming motor 813 to thezooming motor driver 814.

The drive/stop signal and the rotating-direction instruction signalcorrespond to the switch state of the zoom switch 823, and the zoomingmotor driver 814 sets the phase order of four motor excitation phases toa phase order for forward rotation or a phase order for reverse rotationaccording to the rotating-direction instruction signal supplied from theAF microcomputer 812, and outputs voltages (or currents) for therespective four motor excitation phases to the zooming motor 813 whilevarying the voltages (or the currents), according to the drive/stopsignal supplied from the AF microcomputer 812.

Thus, the rotating direction and rotating frequency of the zooming motor813 are controlled, while the zooming motor driver 814 turns on/off itsoutput to the zooming motor 813 according to the aforesaid drive/stopsignal.

The position of the focusing lens 105 is detected by a position encoder815, and the detection result is appropriately gain-controlled by anamplifying circuit 816 and supplied from the amplifying circuit 816 to acomparing circuit 817.

In the meantime, a target signal for moving the focusing lens 105 to atarget position is supplied from the AF microcomputer 812 to thecomparing circuit 817.

The comparing circuit 817 compares the signal from the amplifyingcircuit 816 and the target signal from the AF microcomputer 812,generates a deviation signal equivalent to the difference between thetwo signals, and supplies the deviation signal to an integrating circuit818.

The integrating circuit 818 performs integration processing on thedeviation signal supplied from the comparing circuit 817, and suppliesthe integral result to an adding circuit 819.

At this time, the detection result outputted from the position encoder815 is differentiated by a differentiating circuit 820, and thedifferential result outputted from the differentiating circuit 820,i.e., information indicative of the current driving speed of thefocusing lens 105, is also supplied to the adding circuit 819.

The adding circuit 819 adds together the integral result of theintegrating circuit 818 and the differential result of thedifferentiating circuit 820, and sends the sum to a motor driver 821.

The motor driver 821 applies to a motor coil 822 a current according tothe sum supplied from the adding circuit 819.

At this time, a reference voltage is applied to one end of the motorcoil 822.

Accordingly, the motor driver 821 applies to the other end (to which thereference voltage is not applied) of the motor coil 822 a voltage whichis positive or negative with respect to the reference voltage, therebyswitching the polarity of the current flowing through the motor coil 822to change the moving direction of the focusing lens 105. In addition,the motor driver 821 varies the levels of the voltages applied to themotor coil 822, thereby varying the amount of driving of the focusinglens 105.

Loop control is performed in the above-described manner. The purpose offeeding back the driving speed of the focusing lens 105 (thedifferential result of the differentiating circuit 820) by means of thedifferentiating circuit 820 is to stabilize the entire loop system andto inhibit an abrupt movement of the focusing lens 105 so that a naturalpicked-up image is obtained as well as so that the focusing lens 105 canbe prevented from moving beyond its movable range and colliding with amechanical member of an image pickup apparatus 800.

The target signal supplied from the AF microcomputer 812 to thecomparing circuit 817 is generated by referring to a data table for adesired position to which the focusing lens 105 is to be moved. The datatable contains, for example, the correlation between the output level ofthe target signal and the position of the focusing lens 105, and ispreviously stored in the AF microcomputer 812.

The zooming-operation control processing of the AF microcomputer 812will be described below.

The AF microcomputer 812 is arranged to execute zooming-operationcontrol processing once during one vertical synchronizing period inaccordance with the flowchart shown in FIG. 31 by way of example.

FIG. 32 is a flowchart specifically showing the processing of Step S205of FIG. 31, and FIG. 33 is a flowchart specifically showing theprocessing of Step S301 of FIG. 32.

FIG. 34 is a flowchart specifically showing the processing of step S214of FIG. 31.

FIG. 35 shows a data table TB of cam locus information, such as thatshown in FIG. 3, which is stored in the AF microcomputer 812.

FIG. 35 shows in-focus position data A(n, v) for the focusing lens 105for each subject distance, and the in-focus position of the focusinglens 105 varies according to the position of the variator lens 102 foreach subject distance.

As shown in the data table TB, the position of the focusing lens 105(subject distance) varies along the column of a variable (subjectdistance variable) n, and the position of the variator lens 102 (focallength) varies along the row of a variable (hereinafter referred to asan area or zoom area variable) v.

In this data table TB, n=0 represents the subject distance of a subjectlying at infinity, and as n becomes larger, the subject distance variestoward a closest distance, and n=m represents a subject distance of 1cm. Further, v=0 represents the position of the variator lens 102 lyingat the wide-angle end, and as v becomes larger, the focal lengthincreases, and v=s represents the position of the variator lens 102lying at the telephoto end. According to the data table, one cam locusis drawn with one column of table data.

The zooming-operation control processing of the AF microcomputer 812will be described below with reference to FIGS. 31 to 35.

First, the AF microcomputer 812 starts the zooming-operation controlprocessing (Step S201) and reads a switch state of the zoom switch 823(Step S202).

Then, the AF microcomputer 812 determines (Step S203) whether zooming isbeing executed, in accordance with the state of the zoom switch 823which has been read in Step S202. If zooming is not being executed, theAF microcomputer 812 executes control for inhibiting the driving of thevariator lens 102 and waits for the arrival of the next verticalsynchronizing period (Step S216).

On the other hand, if zooming is being executed, the AF microcomputer812 sets a zooming-operation driving speed (zooming speed) Zsp of thezooming motor 813 (Step S204), and executes Step S205 and the followingprocessing.

Specifically, the distance to a subject which is being photographed isidentified on the basis of the current positions of the variator lens102 and the focusing lens 105, and information indicative of theidentified subject distance is stored as three locus parameters α, β andγ in a RAM (random access memory) (not shown) or the like provided inthe AF microcomputer 812 (Step S205).

The processing of Step S205 will be specifically described below. Asshown in FIG. 32, for example, if an in-focus state is maintained withrespect to the current positions of the variator lens 102 and thefocusing lens 105, it is calculated (Step S301) which of the zoom areasv on the data table TB of FIG. 35 corresponds to a current position Zxof the variator lens 102, the zoom areas v being obtained by dividingthe entire zoom area from the wide-angle end to the telephoto end into sequal areas,

Step S301 will be specifically described below with reference to FIG.33. Referring to FIG. 33, first, the zoom area variable v is cleared(Step S401).

Then, in Step S402, a zoom position Z(v) of the focusing lens 105 at aboundary in the area v is calculated by using the following equation:

Z(v)=(zoom position for telephoto end−zoom position for wide-angleend)×v/s+zoom position for wide-angle end.  (21)

This position Z(v) corresponds to any one of the positions Z0, Z1, Z2, .. . of the variator lens 102 which are shown in FIG. 4 describedpreviously.

Then, it is determined (Step S403) whether the zoom position Z(v)obtained in Step S402 is equal to a current zoom position Zx of thevariator lens 102. If the zoom position Z(v) is equal to the zoomposition Zx, it is determined (Step S407) that the zoom position Zx ofthe variator lens 102 lies on the boundary in the zoom area v, and aboundary flag is set to 1 (Step S407).

If the answer in Step S403 is false, it is determined whether the zoomposition Z(v) calculated in Step S402 is greater than the currentposition Zx of the variator lens 102 (Step S404). If the answer in StepS404 is true, it is determined that the current position Zx of thevariator lens 102 lies between Z(v−1) and Z(v), and the boundary flag isset to 0 (Step S406).

If the answer in Step S404 is false, the area (variable) v isincremented (v=v+1), and the process returns to Step S402.

When the above-described steps S401 to S407 are repeatedly performed andthe processing of Step S301 which includes Step S401 to S407 iscompleted, it can be determined whether the current position Zx of thevariator lens 102 is present in the k-th zoom area v on the data tableTB shown in FIG. 35 and is present at a boundary in the k-th zoom areav.

When the area v is determined in the above-described processing of StepS301, it is calculated in Step S302 and the following processing wherethe position of the focusing lens 105 is on the data table TB shown inFIG. 35.

First, the subject distance variable n is cleared (Step S302).

Then, it is determined from the value of the aforesaid boundary flagwhether the current position Zx of the variator lens 102 is present at aboundary in the k-th zoom area v (Step S303). If the value of theboundary flag is 0, it is determined that the current position Zx doesnot lie on the boundary, and Zk←Z(v) and Zk−1←Z(v−1) are set (StepS305).

Then, four table data A(n, v−1), A(n, v), A(n+1, v−1) and A(n+1, v) areread from the data table TB shown in FIG. 35 (Step S306), and ax and bxare calculated from the respective equations (2) and (3) described above(Step S307).

On the other hand, if it is determined in Step S303 that the value ofthe boundary flag is 1, it is determined that current position Zx of thevariator lens 102 is present at the boundary, and the subject distance nand the in-focus positions A(n, v) and A(n+1, v) are read from the datatable TB shown in FIG. 35, and memorized as ax and bx, respectively(Step S304).

If ax and bx are obtained in the processing of Step S307 or Step S304,then it is determined whether a current position Px of the focusing lens105 is not less than ax (Step S308).

If the answer in Step S308 is true, it is determined whether the currentposition Px of the focusing lens 105 is not less than bx (Step S309).

If the answer in Step S309 is false, the following setting is performed:

α=Px−ax (Step S313),

β=bx−ax (Step S314), and

γ=n (Step S315).

If the answer in Step S308 is false, it is determined that the currentposition Px of the focusing lens 105 is at ultra infinity and the locusparameter α is set to α=0 (Step S312). Then, the above-describedprocessing of Steps S314 and S315 is performed, and locus parameters forinfinity are stored in the RAM.

If the answer in Step S309 is true, it is determined that the positionPx of the focusing lens 105 is closer to the closest-distance end, andthe subject distance n is incremented (n=n+1) (Step S310).

Then, it is determined whether the subject distance n is not greaterthan a closest subject distance m (Step S311). If the answer is true,the process returns to Step S303.

If the answer in Step S311 is false, it is determined that the positionPx of the focusing lens 105 is at an ultra close distance, and theprocess proceeds to Step S312 and the following processing, in which thelocus parameters α, β and γ for the closest distance are stored in theRAM.

Through Step S205 of FIG. 31 which includes the above-described stepsS301 to S315, the locus parameters α, β and γ are stored in the RAMwhich indicate at which position on the cam loci shown in FIG. 2 thecurrent positions of the variator lens 102 and the focusing lens 105 arepresent.

Then, a zoom position Zx′ to be reached by the variator lens 102 afterone vertical synchronizing period is calculated (Step S206).

Letting Zsp (pps) be the zooming speed set in Step S204, the zoomposition Zx′ to be reached by the variator lens 102 after one verticalsynchronizing period is given by the following equation (22):

Zx′=Zx±Zsp/(vertical synchronizing frequency).  (22)

In Equation (22), the unit “pps” represents the rotating speed of thezooming motor 813, i.e., a stepping motor, and indicates the number ofsteps per second of the stepping motor during rotation (1 step=1 pulse).The sign “±” used in Equation (7) indicates different moving directionsof the variator lens 102, and the sign “+” indicates that the variatorlens 102 moves toward the telephoto end, while the sign “−” indicatesthat the variator lens 102 moves toward the wide-angle end.

Then, it is determined in which area v′ the position Zx′ calculated inStep S206 is present (Step S207).

Step S207 is a processing similar to that shown in FIG. 32, and Zx→Zx′and v→v′ are set in a manner similar to that shown in FIG. 32.

Then, on the basis of the value of the boundary flag which has been setin Step S207, it is determined whether the position Zx′ of the variatorlens 102 after 1V (one vertical synchronizing period) is present at aboundary in the area v′ (Step S208). If the value of the boundary flagis 0, it is determined that the position Zx′ is not present at aboundary, and Zk←Z(v′) and Zk−1←Z(v′−1) are set (Step S209).

Then, four table data A(γ, v′−1), A(γ, v′), A(y+1, v′−1) and A(γ+1, v′)for the subject distance γ identified by the processing shown in FIG. 32are read (Step S210), and ax′ and bx′ are calculated from the respectiveequations (2) and (3) described above (Step S211).

On the other hand, if the value of the boundary flag is 1 in Step S208,it is determined that the position Zx′ is present at a boundary, and thein-focus positions A(γ, v′) and A(γ+1, v′) for the subject distance γand the area v′ are read, and are memorized as ax′ and bx′, respectively(Step S212).

When ax′ and bx′ are obtained in Step S211 or S212, an in-focus positionPx′ to be reached by the focusing lens 105 when the variator lens 102reaches the position Zx′ is calculated (Step S213).

This in-focus focus position Px′, i.e., a target trace position to bereached by the focusing lens 105 after one vertical synchronizingperiod, is calculated by the following equation (23) by using theabove-described equation (1):

Px′=(bx′−ax′)×α/β+ax′.  (23)

Then, the zooming motor driver 814 is controlled so that the zoomingmotor 813 is driven at the zooming speed set in Step S204 (Step S214).

The processing of Step S214 will be specifically described. The drivingof the zooming motor 813 is effected by executing the processing(interrupt processing) of the flowchart shown in FIG. 34 at an interruptperiod corresponding to the driving speed of the zooming motor 813.

As described previously, the driving of the variator lens 102 iseffected by supplying to the zooming motor 813 a frequency signalcorresponding to the driving speed of the zooming motor 813 and adirection signal corresponding to the driving direction of the same.

If this processing (interrupt processing) is started (Step S501), adecision is made as to the current state of driving of the variator lens102 (Step S502). If it is determined that the variator lens 102 is in anon-driven state, the driven state of the variator lens 102 is set to astopped state (Step S509) and the next interrupt period is set (StepS510), and the processing shown in FIG. 34 is completed (Step S511).

If it is determined in Step S502 that the variator lens 102 is in adriven state, i.e., zooming is being executed, it is determined whetherto move the variator lens 102 toward the telephoto end (Step S503).

If it is determined in Step S503 that the variator lens 102 needs to bemoved toward the telephoto end, it is determined that the variator lens102 has already reached the telephoto end (Step S504). If it isdetermined in Step S503 that the variator lens 102 does not need to bemoved toward the telephoto end, i.e., the variator lens 102 needs to bemoved toward the wide-angle end, it is determined that the variator lens102 has already reached the wide-angle end (Step S506).

If it is determined in Step S506 that the variator lens 102 has alreadyreached the wide-angle end, the process proceeds to Step S509, in whichthe movement of the variator lens 102 is inhibited.

If it is determined in Step S504 that the variator lens 102 has alreadyreached the telephoto end, the process similarly proceeds to Step S509,in which the movement of the variator lens 102 is inhibited.

If it is determined in Step S506 that the variator lens 102 has not yetreached the wide-angle end, the driving direction of the zooming motordriver 814 is set to a negative rotating direction and the position Zxof the variator lens 102 is decremented by 1 (Step S507).

If it is determined in Step S504 that the variator lens 102 has not yetreached the telephoto end, the driving direction of the zooming motordriver 814 is set to a positive rotating direction and the position Zxof the variator lens 102 is incremented by 1 (Step S505).

After the processing of Step S507 or S505, the logic of a currentfrequency signal is inverted so that a frequency signal corresponding tothe driving speed of the variator lens 102 can be outputted to thezooming motor driver 814 (Step S508).

Specifically, in the processing of the fourth embodiment, sinceinterrupts are caused in accordance with the driving frequency, theoutput logic for the zooming motor driver 814 is successively invertedin Step S508. Thus, a pulse train corresponding to the driving frequencyis generated, and the zooming motor driver 814 rotates the zooming motor813 by controlling the excitation phase of the zooming motor 813 inaccordance with the switching of the logic of the pulse train and thedriving direction of the zooming motor 813. Thus, the variator lens 102moves in accordance with the rotation of the zooming motor 813.

Then, the next interrupt period is set (Step S510), and the processingshown in FIG. 34 is completed (Step S511).

When the variator lens 102 is moved by the processing of Step S214 whichincludes the above-described steps S501 to S511, the comparing circuit817 is supplied with a target signal which corresponds to the targettrace position Px′ (obtained from Equation (23)) to be reached by thefocusing lens 105 after one vertical synchronizing period (Step S215).

In this manner, the focusing lens 105 is moved to the target position atthe response speed determined by the above-described loop control, andthe focusing lens 105 is held at the target position until the nextupdating of the target position.

By executing the above-described control processing in accordance withthe flowchart of FIG. 31, a destination to be reached by the variatorlens 102 after one vertical synchronizing period is predicted, and atrace destination on a cam locus to be reached by the focusing lens 105according to the position of the destination of the variator lens 102 isdetermined. Accordingly, it is possible to inhibit defocusing during thetracing of a cam locus.

The AF operation control processing of the AF microcomputer 812 will bedescribed below.

Incidentally, in the flowchart of FIG. 36, the driving control of thefocusing lens 105 is carried out by successively updating a targetposition which is a trace destination on a cam locus to be reached bythe focusing lens 105, as described above with reference to theflowchart of FIG. 31.

When the processing is started (Step S601), the AF microcomputer 812executes the control of driving the focusing lens 105 by a small amountthrough a wobbling operation, and obtains the above-described AFevaluation signal to determine whether the current state of focus is anin-focus state or an out-of-focus state (Step S602).

Incidentally, if it is determined that the state of focus is anout-of-focus state, it is determined whether the state of focus is anear-focus state or a far-focus state.

Then, the AF microcomputer 812 determines whether the focusing lens 105is currently in focus, from the result of the wobbling operation of StepS602 (Step S603).

If the AF microcomputer 812 determines in Step S603 that the focusinglens 105 is in focus, the AF microcomputer 812 executes control forstopping the focusing lens 105, and the process proceeds to a restartmonitoring routine (to be described later) which starts from Step S608.

On the other hand, if it is determined that the focusing lens 105 is notin focus, the process proceeds to a hill-climbing operation processingroutine (to be described later) which starts from Step S604.

In the hill-climbing operation processing routine, first of all, the AFmicrocomputer 812 executes the hill-climbing operation of driving thefocusing lens 105 in a defocusing direction in accordance with theresult of the decision made in Step S602, i.e., according to whether thestate of focus is a near-focus state or a far-focus state (Step S604).

Then, the AF microcomputer 812 determines whether an in-focus point,i.e., the peak of the AF evaluation signal has been passed (Step S605).If it is determined that the peak of the AF evaluation signal has notbeen passed, the process returns to Step S604 in which the AFmicrocomputer 812 continues the hill-climbing operation.

If the AF microcomputer 812 determines in Step S605 whether the peak hasbeen passed, the AF microcomputer 812 executes the driving control ofthe focusing lens 105 so as to return the level of the AF evaluationsignal to the peak (Step S606).

Then, the AF microcomputer 812 determines whether the level of the AFevaluation signal has reached the peak (Step S607), and if it isdetermined that the level of the AF evaluation signal has not reachedthe peak, the process returns to Step S606.

If it is determined in Step S607 that the level of the AF evaluationsignal has reached the peak, the process returns to Step S602.

While the operation of returning the level of the AF evaluation signalto the peak is being performed, the state of a subject may vary, as bypanning. For this reason, when the level of the AF evaluation signalreaches the peak, the process returns to Step S602 to again execute awobbling operation in order to determine whether the current level ofthe AF evaluation signal has certainly reached the peak, i.e., whetherthe current position of the focusing lens 105 is an in-focus point.

In the restart monitoring routine, first, the AF microcomputer 812memorizes the signal level of the AF evaluation signal level obtainedduring the in-focus state (Step S608).

Then, the AF microcomputer 812 determines whether the current signallevel of the AF evaluation signal has varied compared to the signallevel of the AF evaluation signal memorized in Step S608 during thein-focus state (step S609).

For example, if the current signal level of the AF evaluation signal hasvaried by not less than a predetermined percent with respect to thememorized signal level, it is determined that the state of the subjecthas changed, as by panning, and the driving of the focusing lens 105needs to be restarted. If the amount of variation in the current signallevel of the AF evaluation signal is less than the predeterminedpercent, it is determined that the state of the subject has not changedand the driving of the focusing lens 105 does not need to be restarted.

Then, it is determined whether to restart the driving of the focusinglens 105, according to the result of the decision made in Step S609(Step S610). If a restart of the driving of the focusing lens 105 is notneeded, the AF microcomputer 812 executes control for stopping thefocusing lens 105 is stopped at a position where it is located at thattime (Step S611). Then, the process returns to the restart determiningroutine of Step S609.

On the other hand, if it is determined in Step S610 that a restart ofthe driving of the focusing lens 105 is needed, the process returns toStep S602 and the processing which starts from Step S602, i.e., thewobbling operation, is again performed to determine in which directionto move the focusing lens 105.

By repeating the above-described processing of Step S602 to S611, thefocusing lens 105 is driven so that the in-focus state is maintained atall times.

However, the above-described arrangement has a number of problems. Forexample, in the image pickup apparatus 800 shown in FIG. 30, i.e., aconventional image pickup apparatus using a linear motor for driving afocusing, during any of a hill-climbing operation for focus adjustment,a direction determining operation based on a wobbling operation and ahill-top determining operation, high-speed driving of the focusing lensis carried out in accordance with the response characteristics offeedback loop and the driving is immediately stopped when the focusinglens reaches a target position. For this reason, the repetition of adriven state and a stopped state appears on the picture of an imagebeing picked up, so that a visually impaired video image which exhibitsa non-smooth discontinuous motion is picked up during a movement of thefocusing lens.

In particular, even if the state of focus is to be determined with theamount of driving of the focusing lens being kept within an allowabledepth of field, as in the case of a wobbling operation which is executednear a hill top near an in-focus point, the frequency of switching ofthe focusing lens from the driven state to the stopped state is high. Asa result, if a subject which exceeds an allowable depth of field outsidean in-focus subject distance is present in the picture of an image beingpicked up, the repetition of the driven state and the stopped stateparticularly conspicuously appears on the picture.

In addition, as the amount of movement of the focusing lens to be movedbecomes larger, current energy to be applied to the linear motor becomeslarger, so that, for example, even if the focusing lens reaches a targetposition, the focusing lens overshoots the target position. Accordingly,the oscillation of the focusing lens at the target position increasesand the time required for the focusing lens to stabilize at the targetposition becomes longer. Accordingly, a focus voltage signal accordingto an in-focus position is affected by the oscillation, and amalfunction may also be induced. The oscillation may also appear asdefocusing on the picture of an image being picked up. Furthermore,since the positional error of an actual arrival position relative to thetarget position becomes large, a deviation occurs between therecognition of the position of the focusing lens by a lens controlmicrocomputer or the like and an actual recognition of the position ofthe focusing lens, so that a problem occurs such as impairment of an AFoperation.

Furthermore, in a zooming operation, before the variator lens reaches apredicted position after one vertical synchronizing period, the focusinglens may reach a focus correction position relative to the predictedposition, and if an image which is not blurred is picked up byphotography using a low variation rate in an angle of view such aslow-speed zooming, defocusing may become visible by an amount equivalentto the difference between the arrival times of the variator lens and thefocusing lens.

Furthermore, if the respective lens positions of the focusing andvariator lenses are controlled by actuators having different responsecharacteristics, for example, a linear motor is used as an actuator fordriving the focusing lens and a stepping motor is used as an actuatorfor driving the variator lens, it is difficult to establishsynchronization such as adjustment of stop positions of both lenses.

Specifically, if a stepping motor is used as an actuator for driving thefocusing lens, the focusing lens is moved at an optimum focus tracingspeed according to the inclination of a cam locus and a variation in theposition of the focusing lens coincides with the slope of the cam locusso that an in-focus state can be maintained with respect to an arbitraryposition of the variator lens. In contrast, if a linear motor or thelike is used, since the above-described loop control is executed, themoving speed of the focusing lens is determined by the responsecharacteristics of a loop, so that it becomes difficult to execute thecontrol of moving the focusing lens at a moving speed at a moving speedaccording to the slope of a cam locus.

Specifically, in a zooming operation with the linear motor, as describedabove, since the position of the variator lens approaches an in-focuspoint within one vertical synchronizing period after the focusing lensreaches a target in-focus position, defocusing occurs for only a shorttime, but does not appear on the picture of an image being picked up.However, in the processing based on the flowchart of FIG. 34, if thevariator lens reaches a zoom end before the position of the variatorlens reaches a predicted position to be reached by the variator lensafter one vertical synchronizing period, the movement of the variatorlens is inhibited before one vertical synchronizing period elapses, sothat the variator becomes unable to approach the predicted position anymore. However, since the focusing lens already reaches a focuscorrection position relative to the above-described predicted position,the time period of occurrence of defocusing becomes long and visibledefocusing occurs when the variator lens reaches th zoom end.

In this manner, although the zooming operation using the linear motorcan realize high-speed zooming because of its superior high-speedperformance, it is difficult to establish synchronization, such asadjustment of the stop positions of both of the focusing lens and thevariator lens, owing to the difference in response performance betweenthe different kinds of actuators for driving the focusing lens and thevariator lens.

Each embodiment to be described later is intended to eliminate theabove-described defects, and its object is to provide an image pickupapparatus, a control method therefor, a storage medium in which suchcontrol method is stored and a lens control apparatus all of which arecapable of realizing comfortable autofocus and zooming operations byenabling pseudo speed control even in the case of lens position controlusing a linear motor.

Another object of each of the following embodiments is to provide animage pickup apparatus, a control method therefor, a storage medium inwhich such control method is stored and a lens control apparatus all ofwhich are capable of realizing a comfortable zooming operation bycorrecting a deviation between the response performances of actuatorshaving different response characteristics, such as a linear motor and astepping motor, even in the case of lens position control using suchactuators.

To achieve the above objects, there is provided an image pickupapparatus which comprises image pickup means, a movable part which ismovable along an optical axis for performing focus adjustment, anactuator for driving the movable part, position-of-movable-partdetecting means for detecting a position of the movable part, focuscontrol means for extracting a predetermined focus signal from an outputof the image pickup means, determining a state of focus and supplying adriving signal which causes the movable part to move toward an in-focusposition, according to the determined state of focus, and positioncontrol means for performing position control of the movable part viathe actuator by updating the driving signal by a plurality of timesduring a predetermined time period so that an average moving speed ofthe movable part during the predetermined time period becomes apredetermined speed.

In addition, the actuator is a linear motor, and the position controlmeans updates a target position n times during the predetermined timeperiod by an amount of movement, s/n, at a time with respect to anamount of movement, s, by which the movable part moves at thepredetermined speed, and uses a driving signal corresponding to theupdated target position as the driving signal to be supplied to thelinear motor by the focus control means.

In addition, there is provided an image pickup apparatus which comprisesimage pickup means including a lens and an image pickup element, anactuator for moving a movable part along an optical axis defined by thelens and the image pickup element, the movable part being either one ofthe lens and the image pickup element, position-of-movable-partdetecting means for detecting a position of the movable part, extractingmeans for extracting a focus voltage signal from an output signal of theimage pickup means, and focus control means for determining whether astate of focus is an in-focus state, according to a signal level of thefocus voltage signal extracted by the extracting means, and supplying adriving signal which causes the movable part to move toward an in-focusposition, to the actuator according to the determined state of focus,the focus control means including first control means for calculating atarget position to which the movable part is made to move, on a firstcontrol cycle according to the signal level of the focus voltage signalextracted by the extracting means, and second control means for updatingthe driving signal to be supplied to the actuator, on a second controlcycle, the second control means executing updating of the driving signalon the second control cycle so that an average moving speed at which themovable part continues to move until the movable part reaches the targetposition calculated by the first control means becomes a predeterminedspeed, as well as so that the movable part gradually approaches thetarget position until the movable part reaches the target position.

In addition, there is provided an image pickup apparatus which comprisesa first lens group for performing a magnification varying operation, asecond lens group and an image pickup element either one of whichconstitutes a movable part for correcting a movement of a focal planeduring a movement of the first lens group, position-of-movable-partdetecting means for detecting a position of the movable part, drivingmeans for driving the movable part by supplying a driving signal to anactuator for moving the movable part along an optical axis, storagemeans for storing, according to a subject distance, an in-focus positionof the movable part relative to a position of the first lens group,predicting means for predicting a destination position to be reached bythe first lens group after a predetermined time period, during themagnification varying operation, calculating means for calculating acorrection position of the movable part for correcting a movement of thefocal plane with respect to the destination position predicted by thepredicting means according to information stored in the storage means,and position control means for performing position control of themovable part so that, after the predetermined time period, the movablepart reaches the correction position calculated by the calculatingmeans, the position control means controlling a movement of the movablepart so that an average moving speed of the movable part during thepredetermined time period becomes a predetermined speed.

In addition, there is provided an arrangement which comprises a firstlens group for performing a magnification varying operation, firstdriving means for moving the first lens group, a second lens group andan image pickup element either one of which constitutes a movable partfor correcting a movement of a focal plane during a movement of thefirst lens group, position-of-movable-part detecting means for detectinga position of the movable part, second driving means for driving themovable part by supplying a driving signal to an actuator for moving themovable part along an optical axis, storage means for storing, accordingto a subject distance, an in-focus position of the movable part relativeto a position of the first lens group, predicting means for predicting adestination position to be reached by the first lens group after apredetermined time period, during the magnification varying operation,calculating means for calculating a correction position of the movablepart for correcting a movement of the focal plane with respect to thedestination position predicted by the predicting means according toinformation stored in the storage means, and position control means forperforming position control of the movable part so that, after thepredetermined time period, the movable part reaches the correctionposition calculated by the calculating means, a moving speed of thefirst lens group being controlled so that a position to be reached bythe first lens group after the predetermined time period becomescoincident with an end position of a movable range of the first lensgroup if the destination position predicted by the predicting meansexceeds the end position.

In addition, there is provided an image pickup apparatus which comprisesa first lens group for performing a magnification varying operation,first driving means for moving the first lens group, a second lens groupand an image pickup element either one of which constitutes a movablepart for correcting a movement of a focal plane during a movement of thefirst lens group, position-of-movable-part detecting means for detectinga position of the movable part, second driving means for driving themovable part by supplying a driving signal to an actuator for moving themovable part along an optical axis, storage means for storing, accordingto a subject distance, an in-focus position of the movable part relativeto a position of the first lens group, and control means for performingposition control of the movable part for correcting a movement of thefocal plane due to a variation in position of the first lens groupduring the magnification varying operation, according to informationstored in the storage means, the movable part being forcedly moved to anin-focus position relative to a stop position of the first lens group atthe instant when the magnification varying operation stops.

In addition, there is provided an image pickup apparatus which comprisesa first lens group for performing a magnification varying operation, asecond lens group and an image pickup element either one of whichconstitutes a movable part for performing focus adjustment as well ascorrecting a movement of a focal plane during the magnification varyingoperation, first control means for performing position control of thefirst lens group to move the first lens group along an optical axis, andsecond control means for performing position control of the movable partto move the movable part along the optical axis, a control cycle of thesecond control means being made shorter than a control cycle of thefirst control means at least if a position of the first lens group ispresent in a predetermined area.

In addition, there is provided a method of controlling an image pickupapparatus, which comprises the steps of causing an actuator to move amovable part along an optical axis defined by a lens and an image pickupelement, the movable part being either one of the lens and the imagepickup element, determining a state of focus, and performing positioncontrol of the movable part so that the movable part moves toward anin-focus position, according to the determined state of focus, a drivingsignal for moving the movable part being given to the actuator whilebeing updated by a plurality of times during a predetermined time periodso that an average moving speed of the movable part during thepredetermined time period becomes a predetermined speed.

In addition, there is provided a method of controlling an image pickupapparatus, which comprises the steps of causing an actuator to move amovable part along an optical axis defined by a lens and an image pickupelement, the movable part being either one of the lens and the imagepickup element, determining whether a state of focus is an in-focusstate, according to a signal level of a focus voltage signal obtainedfrom an output signal of the image pickup element, and performingposition control of the movable part so that the movable part movestoward an in-focus position, according to the determined state of focus,a target position to which the movable part is made to move according tothe signal level of the focus voltage signal being calculated on a firstcontrol cycle, and the driving signal to be given to the actuator beingupdated on a second control cycle so that an average moving speed atwhich the movable part continues to move until the movable part reachesthe calculated target position becomes a predetermined speed, as well asso that the movable part gradually approaches the target position untilthe movable part reaches the target position.

In addition, there is provided a method of controlling an image pickupapparatus, which comprises the steps of causing an actuator to moveeither one of a second lens group and an image pickup element, whichconstitutes a movable part for correcting a movement of a focal planeduring a movement of a first lens group for performing a magnificationvarying operation, along an optical axis defined by the second lensgroup and the image pickup element, predicting a destination position tobe reached by the first lens group after a predetermined time periodduring the magnification varying operation, and calculating a correctionposition of the movable part for correcting a movement of the focalplane with respect to the predicted destination position of the firstlens group, by means of a memory which stores an in-focus position ofthe movable part relative to a position of the first lens groupaccording to a subject distance, and performing position control of themovable part so that, after the predetermined time period, the movablepart reaches the calculated correction position, a movement of themovable part being controlled so that an average moving speed of themovable part during the predetermined time period becomes apredetermined speed.

In addition, there is provided a method of controlling an image pickupapparatus, which comprises the steps of causing an actuator to moveeither one of a second lens group and an image pickup element, whichconstitutes a movable part for correcting a movement of a focal planeduring a movement of a first lens group for performing a magnificationvarying operation, along an optical axis defined by the second lensgroup and the image pickup element, predicting a destination position tobe reached by the first lens group after a predetermined time periodduring the magnification varying operation, and calculating a correctionposition of the movable part for correcting a movement of the focalplane with respect to the predicted destination position of the firstlens group, by means of a memory which stores an in-focus position ofthe movable part relative to a position of the first lens groupaccording to a subject distance, and performing position control of themovable part so that, after the predetermined time period, the movablepart reaches the calculated correction position, a moving speed of thefirst lens group being controlled so that a position to be reached bythe first lens group after the predetermined time period becomescoincident with an end position of a movable range of the first lensgroup if the destination position predicted by the predicting meansexceeds the end position.

In addition, there is provided a method of controlling an image pickupapparatus, which comprises the steps of causing an actuator to moveeither one of a second lens group and an image pickup element, whichconstitutes a movable part for correcting a movement of a focal planeduring a movement of a first lens group for performing a magnificationvarying operation, along an optical axis defined by the second lensgroup and the image pickup element, predicting a destination position tobe reached by the first lens group after a predetermined time periodduring the magnification varying operation, and calculating a correctionposition of the movable part for correcting a movement of the focalplane with respect to the predicted destination position of the firstlens group, by means of a memory which stores an in-focus position ofthe movable part relative to a position of the first lens groupaccording to a subject distance, and performing position control of themovable part so that, after the predetermined time period, the movablepart reaches the calculated correction position, the movable part beingforcedly moved to an in-focus position relative to a stop position ofthe first lens group at the instant when the magnification varyingoperation stops.

In addition, there is provided a method of controlling an image pickupapparatus which performs position control of a first lens group forperforming a magnification varying operation and either one of a secondlens group and an image pickup element, which constitutes a movable partfor performing focus adjustment as well as correcting a movement of afocal plane during the magnification varying operation, so that thefirst lens group and the movable part are respectively moved along anoptical axis, a control cycle of the movable part being made shorterthan a control cycle of the first lens group at least if a position ofthe first lens group is present in a predetermined area.

In addition, there is provided an arrangement which comprises a movablepart which is movable along an optical axis for performing focusadjustment, an actuator for driving the movable part,position-of-movable-part detecting means for detecting a position of themovable part, focus control means for determining a state of focus andsupplying to the actuator a driving signal which causes the movable partto move toward an in-focus position, according to the determined stateof focus, and position control means for performing position control ofthe movable part via the actuator by updating the driving signal by aplurality of times during a predetermined time period so that an averagemoving speed of the movable part during the predetermined time periodbecomes a predetermined speed.

Fourth Embodiment

A fourth embodiment of the present invention will be described belowwith reference to the accompanying drawings.

A method of controlling an image pickup apparatus according to thefourth embodiment of the present invention is carried out by using theimage pickup apparatus 100 shown in FIG. 18 by way of example.

The image pickup apparatus 100 is one example to which the image pickupapparatus or the lens control apparatus according to the presentinvention is applied, and a storage medium according to the presentinvention is applied to various processing programs built in the lenscontrol microcomputer 112 (which will be described later) of the imagepickup apparatus 100.

As shown in FIG. 18, the image pickup apparatus 100 adopts an innerfocus type of lens system which includes the fixed first lens group 101,the second lens group (variator lens) 102 arranged to perform amagnification varying operation, the iris 103, the fixed third lensgroup 104, and the fourth lens group (focusing lens) 105 which has botha focus adjusting function and the function of correcting the movementof a focal plane (compensation function).

The image pickup apparatus 100 also includes the image pickup element106 on which image light passing through the aforesaid lens system isfocused, the amplifier 107 to which the output of the image pickupelement 106 is supplied, a camera signal processing circuit 108, an iriscontrol circuit 128, the AF signal processing circuit 109, the output ofthe amplifier 107 being supplied to each of the circuits 108, 128 and109, the lens control microcomputer 112 to which the output of the AFsignal processing circuit 109 is supplied, the timing generator 111, andthe AF frame generating circuit 110 to which the output of the timinggenerator 111 is supplied. The output of the AF frame generating circuit110 is supplied to the AF signal processing circuit 109, while theoutput of the lens control microcomputer 112 is supplied to the AF framegenerating circuit 110, and a video signal obtained by picking up animage is outputted from the camera signal processing circuit 108.

The image pickup apparatus 100 also includes the position encoder 1502for detecting the positional state of the focusing lens 105, theamplifying circuit 1503 and the differentiating circuit 1506 to each ofwhich the output of the position encoder 1502 is supplied, the comparingcircuit 1504 to which the output of the amplifying circuit 1503 and theoutput of the lens control microcomputer 112 are supplied, theintegrating circuit 1505 to which the output of the comparing circuit1504 is supplied, the adding circuit 1507 to which the output of thedifferentiating circuit 1506 and the output of the integrating circuit1505 are supplied, the motor driver 1508 to which the output of theadding circuit 1507 is supplied, and the motor 1501 for the focusinglens 105 to which the output of the motor driver 1508 is supplied. Theoutput of the position encoder 1502 is also supplied to the lens controlmicrocomputer 112.

The image pickup apparatus 100 further includes the motor driver 118 towhich the output of the lens control microcomputer 112 is supplied, themotor 117 for the variator lens 102 to which the output of the motordriver 118 is supplied, the iris driver 123 to which the output of theiris control circuit 121 is supplied, and the IG meter 122 to which theoutput of the iris driver 123 is supplied.

A sequence of operations of the above-described image pickup apparatus100 will be described below.

Light (image light) from a subject (not shown) passes through the firstlens group 101, the variator lens 102, the iris 103, the third lensgroup 104 and the focusing lens 105 in that order, and is focused on theimage pickup surface of the image pickup element 106 made from a CCD orthe like. The focused image light is converted into a video signal byphotoelectric conversion in the image pickup element 106, and the videosignal is supplied to the amplifier 107.

The amplifier 107 amplifies the video signal supplied from the imagepickup element 106 to an optimum signal level, and supplies theamplified signal to the camera signal processing circuit 108.

The camera signal processing circuit 108 performs predetermined signalprocessing on the video signal supplied from the amplifier 107, andgenerates a standard television signal. The camera signal processingcircuit 108 outputs th standard television signal to, for example, adisplay part or a recording part (not shown).

The video signal amplified by the amplifier 107 is also supplied to eachof the AF signal processing circuit 109 and the iris control circuit121.

The iris control circuit 121 drives and controls the IG meter 122 viathe iris driver 123 according to the level of the video signal suppliedfrom the amplifier 107, thereby making adjustment of the amount of lightat the iris 103.

At this time, the AF frame generating circuit 110 generates a gatesignal for gating a predetermined area of an image picked up on theimage pickup surface of the image pickup element 106, in response tovertical and horizontal synchronizing signals supplied from the timinggenerator 111 in accordance with AF-frame control (to be describedlater) provided by the lens control microcomputer 112, and outputs thegate signal to the AF signal processing circuit 109.

The AF signal processing circuit 109 extracts only a high-frequencycomponent of the video signal contained in an AF frame from the videosignal supplied from the amplifier 107, in response to the gate signalsupplied from the AF frame generating circuit 110, and performspredetermined processing such as the processing of generating an AFevaluation signal.

The lens control microcomputer 112 is an AF microcomputer for lenscontrol, and includes, for example, the AF program 113 for making focusadjustment according to the strength of the AF evaluation signalgenerated by the AF signal processing circuit 109, the zoom controlprogram 114 for maintaining the focusing lens 105 in an in-focus statewhile causing the focusing lens 105 to trace a cam locus, the lens camdata 115 to be referred to by the lens control microcomputer 112 duringthe tracing of a cam locus, the zooming motor control program 116 fordriving the variator lens 102 during zooming, and a focus controlprogram 119 for driving the focusing lens 105 during AF. The lenscontrol microcomputer 112 is arranged to perform control of lensdriving, AF frame control for varying a distance measuring area, and thelike.

Incidentally, various processing programs such as the AF program 113,the zoom control program 114, the lens cam data 115, the zooming motorcontrol program 116 and the focus control program 119 may also be storedin, for example, a ROM (read-only memory) which is externally connectedto the apparatus.

The AF microcomputer 112 is arranged to be supplied with informationindicative of the switch state of each of a zoom switch 131 and an AFswitch 132 which are provided on the apparatus, and executes theaforesaid various programs on the basis of such switch-stateinformation, thereby carrying out various control processing such as thecontrol of lens driving and the AF frame control.

The lens control microcomputer 112 supplies an instruction to drive thevariator lens 102 to the motor driver (hereinafter referred to as thezooming motor driver) 118, in accordance with the switch state of thezoom switch 131, thereby causing the zooming motor driver 118 to drivethe motor (hereinafter referred to as the zooming motor) 117 forvariator lens 102.

The zooming motor 117 consists of, for example, a stepping motor, anddetermines the driving speed of the zooming motor 117 by executing thezooming motor control program 116 and supplies the determined drivingspeed to the zooming motor driver 118 as a rotating-frequency signal forthe zooming motor 117.

The lens control microcomputer 112 also supplies a drive/stop signal anda rotating-direction instruction signal for the zooming motor 117 to thezooming motor driver 118.

The drive/stop signal and the rotating-direction instruction signalcorrespond to the switch state of the zoom switch 131, and the zoomingmotor driver 118 sets the phase order of four motor excitation phases toa phase order for forward rotation or a phase order for reverse rotationaccording to the rotating-direction instruction signal supplied from thelens control microcomputer 112, and outputs voltages (or currents) forthe respective four motor excitation phases to the zooming motor 117while varying the voltages (or the currents), according to thedrive/stop signal supplied from the lens control microcomputer 112.

Thus, the rotating direction and rotating frequency of the zooming motor117 are controlled, while the zooming motor driver 118 turns on/off itsoutput to the zooming motor 117 according to the aforesaid drive/stopsignal.

The position of the focusing lens 105 is detected by the positionencoder 1502, and the detection result is appropriately gain-controlledby the amplifying circuit 1503 and supplied from the amplifying circuit1503 to the comparing circuit 1504.

In the meantime, a target signal for moving the focusing lens 105 to atarget position is supplied from the lens control microcomputer 112 tothe comparing circuit 1504.

The comparing circuit 1504 compares the signal from the amplifyingcircuit 1503 and the target signal from the lens control microcomputer112, generates a deviation signal equivalent to the difference betweenthe two signals, and supplies the deviation signal to the integratingcircuit 1505.

The integrating circuit 1505 performs integration processing on thedeviation signal supplied from the comparing circuit 1504, and suppliesthe integral result to the adding circuit 1507.

At this time, the detection result outputted from the position encoder1502 is differentiated by the differentiating circuit 1506, and thedifferential result outputted from the differentiating circuit 1506,i.e., information indicative of the current driving speed of thefocusing lens 105, is also supplied to the adding circuit 1507.

The adding circuit 1507 adds together the integral result of theintegrating circuit 1505 and the differential result of thedifferentiating circuit 1506, and sends the sum to the motor driver1508.

The motor driver 1508 applies to the motor 1501 a current according tothe sum supplied from the adding circuit 1507.

The motor 1501 consists of, for example, a linear motor such as a movingcoil type of voice coil motor, and is arranged to drive the focusinglens 105 by means of the moving mechanism shown in FIGS. 16(A) and16(B).

Specifically, a reference voltage is applied to one end of the motor(motor coil) 1501. The motor driver 1508 applies to the other end (towhich the reference voltage is not applied) of the motor coil 1501 avoltage which is positive or negative with respect to the referencevoltage, thereby switching the polarity of the current flowing throughthe motor coil 1501 to change the moving direction of the focusing lens105. In addition, the motor driver 1508 varies the levels of thevoltages applied to the motor coil 1501, thereby varying the amount ofdriving of the focusing lens 105.

Loop control is performed in the above-described manner. The purpose offeeding back the driving speed of the focusing lens 105 (thedifferential result of the differentiating circuit 1506) by means of thedifferentiating circuit 1506 is to stabilize the entire loop controlsystem and to inhibit an abrupt movement of the focusing lens 105 sothat a natural picked-up image is obtained as well as so that thefocusing lens 105 can be prevented from moving beyond its movable rangeand colliding with a mechanical member of the image pickup apparatus100.

The target signal supplied from the lens control microcomputer 112 tothe comparing circuit 1504 is generated by referring to a data table fora desired position to which the focusing lens 105 is to be moved. Thedata table contains, for example, the correlation between the outputlevel of the target signal and the position of the focusing lens 105,and is previously stored in the lens control microcomputer 112.

The driving control of the focusing lens 105 in the AF mode will bedescribed below.

In the image pickup apparatus 100, the present invention is applied to asteady moving operation of the focusing lens 105, such as ahill-climbing operation, and the motor coil 1501 for driving thefocusing lens 105, i.e., the linear motor, is driven so that the averagemoving speed of the focusing lens 105 becomes a predetermined speedduring the AF mode.

The focus control program 119 contains, for example, a processingprogram based on the flowchart of FIG. 36, and this processing programis executed by the lens control microcomputer 112. In the fourthembodiment, the processing contents of Step S604 (hill-climbingoperation) and Step S606 (the operation of returning the position of thefocusing lens 105 to “the top of the hill”) in the above-describedflowchart are greatly different from the conventional ones.

FIG. 19 is a flowchart specifically showing the processing of Step S604in the fourth embodiment, and as shown in FIG. 19, the processing ofStep S604 is similar to that of Step S606.

FIG. 20 is a flowchart showing the processing of generating a targetsignal to be supplied from the lens control microcomputer 112 to thecomparing circuit 1504.

Processing steps to be executed before and after Steps S604 and S606have been described previously, and the detailed description of theprocessing steps is omitted.

As shown in FIG. 19, first, the lens control microcomputer 112 reads anAF evaluation signal (focus voltage signal) relative to the currentposition of the focusing lens 105 (Step S701) and determines whether thesignal level of the read AF evaluation signal is greater than athreshold A (Step S702).

If it is determined in Step S702 that the signal level of the AFevaluation signal is greater than the threshold A, the lens controlmicrocomputer 112 determines whether the signal level of the AFevaluation signal is greater than a threshold B (Step S703).

If it is determined in Step S703 that the signal level of the AFevaluation signal is greater than the threshold B, i.e., the signallevel of the AF evaluation signal is greater than each of the thresholdsA and B, the lens control microcomputer 112 determines that the focusinglens 105 is positioned near the top of the hill and is approximately infocus (defocused to a small extent), and executes the processing of StepS704 which will be described later.

If it is determined in Step S703 that the signal level of the AFevaluation signal is not greater than the threshold B, i.e., the signallevel of the AF evaluation signal is greater than the threshold A and isless than the threshold B, the lens control microcomputer 112 determinesthat the focusing lens 105 is positioned halfway up the hill anddefocused to a medium extent. Then, the lens control microcomputer 112executes the processing of Step S705 which will be described later.

If it is determined in Step S702 that the signal level of the AFevaluation signal is not greater than the threshold A, the lens controlmicrocomputer 112 determines that the focusing lens 105 is positioned atthe foot of the hill and defocused to a great extent. Then, the lenscontrol microcomputer 112 executes the processing of Step S706 whichwill be described later.

In the above-described hill-climbing operation, it is desirable tocontrol the moving speed of the focusing lens 105 so that the positionof the focusing lens 105 can move as fast as possible near the foot ofthe hill.

In this case, an image is picked up in a defocused state, so that themovement of the focusing lens 105 is not visually observed.

In addition, it is desirable to control the moving speed of the focusinglens 105 so that as the focusing lens 105 approaches the top of thehill, the moving speed of the focusing lens 105 is decreased so as toprevent the motion of the focusing lens 105 from appearing on apicked-up image.

If it is determined through Step S702 and Step S703 that the focusinglens 105 is defocused to a great extent, the moving speed per unit time,Vf, of the focusing lens 105 is set to a maximum speed Vfmax to whichthe focusing lens 105 can respond (Step S706). If the focusing lens 105is defocused to a medium extent, the moving speed Vf is set to Vfmax/2(Step S705). If the focusing lens 105 is defocused to a small extent,the moving speed Vf is set to Vfmax/4 (Step S704).

After the completion of all of the above-described steps, the processproceeds to Step S605 or S607 of FIG. 36, in which the processing ofStep S701 to Step S706 shown in FIG. 19 is repeated until the positionof the focusing lens 105 passes or returns to the top of the hill. Thus,the moving speed of the focusing lens 105 is controlled according to thesignal level of the AF evaluation signal.

During the above-described processing according to the flowchart of FIG.19, the updating of the position of the focusing lens 105 is performedby processing according to the flowchart shown in FIG. 20.

It is assumed here that although the processing shown in FIG. 19 isperformed sixty times per unit time (in the case of the NTSC system) insynchronism with each vertical synchronizing period, the processingshown in FIG. 20 is performed n times per unit time at a processingcycle shorter than the cycle of the processing shown in FIG. 19.

First, if the processing of FIG. 20 is started (Step S707), the amountof movement, ΔF, by which the focusing lens 105 is moved each time theprocessing shown in FIG. 20 is executed once is calculated (Step S708).

The amount of movement ΔF is calculated with Equation (24) by using themoving speed per unit time, Vf, of the focusing lens 105 obtained in theprocessing of FIG. 19:

ΔF=Vf/n.  (24)

Then, a target position Fx to which the focusing lens 105 is to be movedis calculated from a current position F0 of the focusing lens 105 byusing Equation (25) (Step S709):

Fx=F 0±ΔF.  (25)

The sign “±” used in Equation (25) indicates different moving directionsof the focusing lens 105, and the sign “+” indicates the movement of thefocusing lens 105 toward the closest-distance end, while the sign “−”indicates the movement of the focusing lens 105 toward the infinity end.The driving direction in which to move the focusing lens 105 is obtainedfrom the result of the wobbling operation or a direction in which toreturn the position of the focusing lens 105 to the top of the hill, inthe processing of the flowchart shown in FIG. 36.

Accordingly, a driving voltage signal corresponding to the targetposition Fx obtained in Step S709 is supplied from the lens controlmicrocomputer 112 to the comparing circuit 1504, and the movement of thefocusing lens 105 is performed by the feedback loop system.

As the above-described processing of Step S707 to Step S709 isrepeatedly performed, the moving speed of the focusing lens 105 per onecycle becomes a moving speed determined by feedback loopcharacteristics, while the average moving speed of the focusing lens 105for one vertical synchronizing period becomes equivalent to the movingspeed Vf obtained by the above-described processing shown in FIG. 19.

Accordingly, if a linear motor is used as the motor 1501 for driving thefocusing lens 105, pseudo control of the speed of the focusing lens 105is performed so that a smooth focus adjustment operation can beperformed.

Fifth Embodiment

A fifth embodiment of the present invention will be described below.

In the above description of the fourth embodiment, reference has beenmade to the example in which the present invention is applied to thesteady moving operation of the focusing lens 105, such as ahill-climbing operation, in the image pickup apparatus 100 shown in FIG.18. In the following description of the fifth embodiment, reference willbe made to an example in which the present invention is applied to awobbling operation in a case where the amount of movement of thefocusing lens 105, i.e., the amount of movement which is equivalent toan amplitude for the wobbling operation, is determined.

As in the case of the above-described fourth embodiment, the processingprogram based on the above-described flowchart of FIG. 36 is containedin, for example, the focus control program 119, and the processingprogram is executed by the lens control microcomputer 112. However, inthe fifth embodiment, the processing contents of Step S602 greatlydiffer from those of Step S602 which have been described above withreference to FIG. 36.

FIG. 21 is a flowchart specifically showing the processing of Step S602according to the fifth embodiment.

FIG. 22 is a flowchart showing the processing of performing positioncontrol of the focusing lens 105 during a wobbling operation. Aprocessing program based on this flowchart is also contained in thefocus control program 119, and is executed by the lens controlmicrocomputer 112.

The wobbling operation and its amplitude will be described below withreference to FIG. 23 before the wobbling operation according to thefifth embodiment is described with reference to FIGS. 21 and 22.

FIG. 23 is a graph showing a hill 1701 representative of a variation inthe signal level of an AF evaluation signal obtained when the focusinglens 105 is moved from the infinity end to the closest-distance end withrespect to an arbitrary subject.

In FIG. 23, the horizontal axis represents the position of the focusinglens 105, while the vertical axis represents the signal level of the AFevaluation signal.

An in-focus point lies at a point 1702 at which the signal level of theAF evaluation signal reaches a maximum, and the position of the focusinglens 105 is controlled so that the signal level of the AF evaluationsignal is maintained at the maximum level at all times.

Incidentally, the position of the focusing lens 105 which corresponds tothe point 1702 at which the signal level of the AF evaluation signalreaches the maximum is an in-focus position 1708.

The wobbling operation is performed to determine whether an in-focuspoint is present on a closest-distance side or on an infinity side.

Specifically, the wobbling operation is the operation of obtaining an AFevaluation signal while driving the focusing lens 105 by a small amount,to determine whether the state of focus is currently an in-focus stateor an out-of-focus state, as well as to determine whether theout-of-focus state is a near-focus state or a far-focus state if thestate of focus is the out-of-focus state.

For example, when the current position of the focusing lens 105 is onthe infinity side of the in-focus point (i.e., a position 1709), if thewobbling operation is executed to drive the focusing lens 105 by a smallamount in a direction away from the closest-distance side, i.e., if theposition of the focusing lens 105 is moved as shown at 1703 (the timeaxis extends from the top to the bottom of the sheet surface of FIG.23), the AF evaluation signal shown at 1704 is obtained at that time.

On the other hand, when the current position of the focusing lens 105 ison the closest-distance side of the in-focus point (i.e., a position1710), if the focusing lens 105 is driven by a small amount as shown at1705, the AF evaluation signal shown at 1706 is obtained at that time.

Accordingly, since the signals 1704 and 1706 are out of phase with eachother, if the state of phase is identified, it is possible to determinea direction in which to move the focusing lens 105 toward the in-focuspoint.

If the focusing lens 105 is driven as shown at 1711 by a small amount onthe top of the hill 1701, the amplitude of the AF evaluation signalobtained at that time is small and shows a different waveform, as shownat 1712, compared to either of the signals 1704 and 1705. It is,therefore, possible to determine whether the current state of focus isan in-focus state or an out-of-focus state.

If the wobbling operation is performed near the in-focus point,defocusing may occur depending on the amount of driving amplitude, α, bywhich to drive the focusing lens 105. It is, therefore, necessary toensure a minimum amplitude for which the signal level of the AFevaluation signal can be fully obtained.

On the other hand, if the focusing lens 105 is driven by a small amountnear the foot of the hill 1701, it may not be possible to obtain thesignal level of the AP evaluation signal which is high enough toidentify the moving direction of the focusing lens 105. It is,therefore, desirable to increase the driving amplitude of the focusinglens 105.

In addition, the speed of the above-described wobbling operation is animportant parameter required to invisibly carry out the wobblingoperation.

Specifically, in a case where a plurality of subjects lying at differentdistances are present in a scene whose image is being picked up, even ifa main subject is in focus, other subjects may be defocused to a smallextent. This phenomenon occurs, particularly when the focusing lens 105is positioned on the wide-angle side.

If the driving amplitude at this time is reduced to a minimum amplitudethe amount of which does not exceed a depth of field, a wobblingoperation will be visible since the subjects defocused to a small extentare outside an allowable depth of field.

Particularly if a wobbling operation is performed at a high speed, thestates of images of the subjects defocused to a small extent vary athigh speeds, so that the wobbling operation becomes extremely easilyvisible.

Accordingly, as in the case of wide-angle photography in which aplurality of subjects are easily contained in a scene, if all thesubjects lying at different distances are focused to some extent andhence the signal level of an AF evaluation signal is high, it ispreferable to reduce the speed of the wobbling operation and lengthenthe period of the operation of driving the focusing lens 105 by a smallamount so that image quality can be improved.

In this case, as the period of the wobbling operation is made longer, ittakes a longer time to determine in which direction to drive thefocusing lens 105. However, in the case of wide-angle photography or thelike, since any subject is visible in a considerably focused state,high-speed focusing is not needed.

On the basis of the above description of the wobbling operation, awobbling operation to be executed in the fifth embodiment will bespecifically described below with reference to FIGS. 21 and 22.

Processing steps to be executed before and after Step S602 are asdescribed previously with reference to FIG. 36, and the detaileddescription of the processing steps is omitted.

As shown in FIG. 21, first, the lens control microcomputer 112 reads anAF evaluation signal (Step S801) and determines whether the signal levelof the read AF evaluation signal is greater than a threshold A (StepS802).

If it is determined in Step S802 that the signal level of the AFevaluation signal is greater than the threshold A, the lens controlmicrocomputer 112 determines whether the signal level of the AFevaluation signal is greater than a threshold B (Step S803).

If it is determined in Step S803 that the signal level of the AFevaluation signal is greater than the threshold B, i.e., the signallevel of the AF evaluation signal is greater than each of the thresholdsA and B, the lens control microcomputer 112 determines that the focusinglens 105 is positioned near the top of the hill and is approximately infocus (defocused to a small extent), and executes the processing of StepS804 which will be described later.

If it is determined in Step S803 that the signal level of the AFevaluation signal is not greater than the threshold B, i.e., the signallevel of the AF evaluation signal is greater than the threshold A and isless than the threshold B, the lens control microcomputer 112 determinesthat the focusing lens 105 is positioned halfway up the hill anddefocused to a medium extent. Then, the lens control microcomputer 112executes the processing of Step S805 which will be described later.

If it is determined in Step S802 that the signal level of the AFevaluation signal is not greater than the threshold A, the lens controlmicrocomputer 112 determines that the focusing lens 105 is positioned atthe foot of the hill and defocused to a great extent. Then, the lenscontrol microcomputer 112 executes the processing of Step S806 whichwill be described later.

If it is determined through Step S802 and Step S803 that the focusinglens 105 is defocused to a great extent, the moving speed per unit time,Vf, of the focusing lens 105 is set to a maximum speed Vfmax to whichthe focusing lens 105 can respond, and an amplitude α for a wobblingoperation is set to an amplitude equivalent to twice a depth of field δaccording to the state of the iris 103 (Step S806).

The depth of field δ is selected to be a value which does not allowdefocusing to occur if the position of the focusing lens 105 is movedfrom an in-focus point.

If the focusing lens 105 is defocused to a medium extent, the movingspeed Vf is set to Vfmax/2 and the amplitude α is set to an amplitudeequivalent to the depth of field δ (Step S805).

If the focusing lens 105 is defocused to a small extent, the movingspeed Vf is set to Vfmax/4 and the amplitude α is set to an amplitudeequivalent to half the depth of field δ (Step S804).

In the above-described steps, the moving speed Vf is set according tothe signal level of the AF evaluation signal, but if the focal length isadditionally used as a parameter for speed setting, it becomes easier tooptimize the driving amplitude and the moving speed of the focusing lens105 for all kinds of subjects.

After the completion of Steps S804, S805 and S806, it is determinedwhether the wobbling operation to be presently executed follows StepS607 of FIG. 36 or Step S610 of FIG. 30 (Step S807).

If it is determined in Step S807 that the wobbling operation followsStep S607, i.e., if the signal level of the AF evaluation signal hasreached a peak, the focusing speed Vf of the focusing lens 105 isreduced to half (Step S808), and the process proceeds to Step S809.

If it is determined in Step S807 that the wobbling operation followsStep S610, i.e., if the signal level of the AF evaluation signal has notyet reached the peak, the process directly proceeds to Step S809.

Step S809 and the following steps are provided for executing theprocessing of driving the focusing lens 105 by a small amount, asdescribed previously with reference to FIG. 23.

First, a destination F1 of the focusing lens 105 is obtained by addingthe amplitude α of the wobbling operation to the current position F0 ofthe focusing lens 105 by using Equation (25) (Step S809):

F 1=F 0+α.  (25)

Then, the focusing lens 105 is driven to move toward theclosest-distance side (Step S810).

Then, it is determined whether the current position F0 of the focusinglens 105 has reached the destination F1 calculated in Step S809 (StepS811). If it is determined in Step S811 that the current position F0 hasnot reached the destination F1, the process returns to Step S810, inwhich the focusing lens 105 is driven to move toward theclosest-distance side.

If it is determined in Step S811 that the current position F0 of thefocusing lens 105 has reached the destination F1 calculated in StepS809, i.e., if the focusing lens 105 is driven by the amplitude α forthe wobbling operation, the signal level of the AF evaluation signal atthis time is stored in a memory Dn (not shown) inside the lens controlmicrocomputer 112 as data for driving the focusing lens 105 toward theclosest-distance side. Then, the destination F1 to be reached by thefocusing lens 105 when the focusing lens 105 is driven toward theinfinity side is calculated by using Equation (26) (Step S812):

F 1=F 0−2α.  (26)

Then, the focusing lens 105 is driven to move toward the infinity side(Step S813).

Then, it is determined whether the current position F0 of the focusinglens 105 has reached the destination F1 set in Step S812 (Step S814). Ifit is determined that the current position F0 has not reached thedestination F1, the process returns to Step S813, in which the focusinglens 105 is driven to move toward the infinity side.

If it is determined in Step S814 that the current position F0 of thefocusing lens 105 has reached the destination F1 set in Step S812, i.e.,if the focusing lens 105 is driven by the amplitude 2α for the wobblingoperation, the signal level of the AF evaluation signal at this time isstored in a memory Df (not shown) inside the lens control microcomputer112 as data for driving the focusing lens 105 toward the infinity side.Then, the destination F1 is again set by calculating Equation (27):

F 1=F 0+α.  (27)

so that the focusing lens 105 is returned to the position at which itwas located before the start of the wobbling operation (Step S815).

Then, the focusing lens 105 is driven to move toward theclosest-distance side (Step S816).

Then, it is determined whether the current position F0 of the focusinglens 105 has reached the destination F1 calculated in Step S815 (StepS817). If it is determined that the current position F0 has not reachedthe destination F1, the process returns to Step S816, in which thefocusing lens 105 is driven to move toward the closest-distance side.

If it is determined in Step S817 that the current position F0 of thefocusing lens 105 has reached the destination F1 calculated in StepS815, i.e., if the focusing lens 105 is driven by the amplitude α forthe wobbling operation, the signal level of the AF evaluation signal atthis time is stored in a memory Dc (not shown) inside the lens controlmicrocomputer 112 as data indicative of an initial position of thefocusing lens 105 (step S818). Thus, the processing shown in FIG. 21 iscompleted, and the process proceeds to Step S603 of FIG. 36.

Then, in Step S603 and the following steps of FIG. 36, hill-climbingdirection determining processing and in-focus position determiningprocessing are performed on the basis of the signal levels of the AFevaluation signals which have been stored in the respective memories Dn,Df and Dc.

While the processing based on the flowchart of FIG. 21 is beingexecuted, the movement of the position of the focusing lens 105 isexecuted by processing based on the flowchart shown in FIG. 22.

Although the processing shown in FIG. 21 is executed, for example, sixtytimes per unit time (in the case of the NTSC system) in synchronism withthe vertical synchronizing period, the processing based on the flowchartof FIG. 22 is executed n times per unit time at a processing cycleshorter than the cycle of the processing shown in FIG. 21 similarly tothe processing based on the flowchart of FIG. 20.

First, if the processing of FIG. 22 is started (Step S819), it isdetermined whether a target position Fx to which the focusing lens 105is to be moved is already equal to the destination F1 (Step S820).

If it is determined in Step S820 that the target position Fx is equal tothe destination F1, the process waits for the next control cycle.

If it is determined in Step S820 that the target position Fx is notequal to the destination F1, the amount of movement, ΔF, by which thefocusing lens 105 is moved each time the processing shown in FIG. 22 isexecuted once is calculated (Step S821).

The amount of movement ΔF is calculated with Equation (28) by using themoving speed per unit time, Vf, of the focusing lens 105 obtained in theprocessing of FIG. 21:

ΔF=Vf/n.  (28)

Then, the target position Fx to which the focusing lens 105 is to bemoved is calculated from the current position F0 of the focusing lens105 by using Equation (29) (Step S822):

Fx=F 0±ΔF.  (29)

The sign “±” used in Equation (29) indicates different moving directionsof the focusing lens 105, and the sign “+” indicates the movement of thefocusing lens 105 toward the closest-distance end, while the sign “−”indicates the movement of the focusing lens 105 toward the infinity end.The driving direction in which to move the focusing lens 105 is obtainedfrom the processing based on the flowchart shown in FIG. 21.

Then, a calculation is performed on the absolute value of the differencebetween the target position Fx calculated in Step S822 and thedestination F1 to be reached by the focusing lens 105 which is driven bya small amount equivalent to the amplitude α for the wobbling operation,and it is determined whether the obtained absolute value is not greaterthan the amount of movement ΔF (calculated in Step S821) by which thefocusing lens 105 is moved each time the processing shown in FIG. 22 isexecuted once (Step S823).

If it is determined in Step S823 that the absolute value is not greaterthan the amount of movement ΔF, it is determined that the currentposition of the focusing lens 105 is sufficiently close to thedestination F1 and, in the next processing cycle, the position of thefocusing lens 105 will pass the destination F1. Accordingly, the targetposition Fx is forcedly set as the destination F1 (Step S824). Then, theprocess returns to Step S820 and waits for the next start of theprocessing.

If it is determined in Step S823 that the absolute value is greater thanthe amount of movement ΔF, it is determined that the current position ofthe focusing lens 105 is still distant from the destination F1.Accordingly, the process returns to Step S820 so that the focusing lens105 can be moved at the desired average moving speed, and waits for thenext start of the processing.

The driving voltage signal corresponding to the target position Fx,which has been obtained in the above-described processing of Steps S819to S824, is supplied from the lens control microcomputer 112 to thecomparing circuit 1504, whereby the focusing lens 105 is driven to moveat the average moving speed while holding the destination F1.

By executing the processing shown in FIGS. 21 and 22, it is possible toperform pseudo speed control of the focusing lens 105 even if thefocusing lens 105 is to be moved by a predetermined amount of movingdistance. Accordingly, for example, even if a small aperture size isselected and the focusing lens 105 needs to be moved by the amount of alarge amplitude, the focusing lens 105 can be moved in such a manner asto gradually approach a predetermined position, whereby the focusinglens 105 can be prevented from oscillating at or overshooting thepredetermined position. Accordingly, it is also possible to move thefocusing lens 105 by a predetermined amount with high precision.

Sixth Embodiment

A sixth embodiment of the present invention will be described below.

In the following description of the sixth embodiment, reference will bemade to an example in which the present invention is applied to azooming operation in the image pickup apparatus 100 shown in FIG. 18.

A processing program based on the flowchart shown in FIG. 24 iscontained in, for example, the zooming motor control program 116, andthe processing program is executed by the lens control microcomputer112.

The processing shown in FIG. 24 is similar to that shown in FIG. 31except that Steps S901 to S903 are incorporated in place of Steps S214and S215 of FIG. 31.

FIG. 24 shows the processing of a zooming operation executed at acontrol cycle equivalent to one vertical synchronizing period, andspecifically shows one example of the processing of controlling theposition of the focusing lens 105 in such a way as to predict a positionto be reached by the variator lens 102 after one vertical synchronizingperiod and correct focus with respect to the predicted position.

In the flowchart shown in FIG. 24, identical reference numbers are usedto denote processing steps similar to those shown in the flowchart ofFIG. 31, and the detailed description thereof is omitted.

FIG. 25 is a flowchart showing driving control processing for thefocusing lens 105 which performs a compensation operation according tothe movement of the variator lens 102, and the processing cycle of theprocessing based on this flowchart is such that the processing isexecuted n times per unit time.

A processing program based on the flowchart of FIG. 25 is also containedin, for example, the zooming motor control program 116, and is executedby the lens control microcomputer 112.

First, as described previously, the destination Px′ to be reached by thefocusing lens 105 after one vertical synchronizing period is determinedby the processing of Steps S201 to S213.

Then, the initializing processing of clearing a counter m to be used inthe processing shown in FIG. 25 is executed, and a current position Pxof the focusing lens 105 is stored in a memory Px0 (not shown) providedin the lens control microcomputer 112 (Step S901).

Then, the amount of movement (Px′−Px) of the focusing lens 105 pervertical synchronizing period is divided by the vertical synchronizingperiod to calculate a compensation speed Vf per unit time (Step S902).

Then, the zooming motor (stepping motor) 117 is driven at the zoomingspeed set in Step S204, thereby moving the variator lens 102 (stepS903). Then, the process returns to Step S202 and waits for the nextprocessing cycle.

While the above-described processing is being executed, the processingshown in FIG. 25 is executed on a processing cycle of n times per unittime.

Specifically, if the processing of FIG. 25 is started (Step S904), thecounter m which has been cleared in Step S901 is incremented (StepS905).

Then, the target position Fx to be reached by the focusing lens 105 eachtime the processing of FIG. 25 is executed once is calculated (StepS906).

This target position Fx is obtained by a calculating method ofsequentially adding the amount of movement, Vf/n, by which the focusinglens 105 is moved each time the processing of FIG. 25 is executed onceto the reference position Px0 at which the focusing lens 105 was presentwhen an in-focus position after one vertical synchronizing period wascalculated.

Specifically, the target position Fx is calculated by using Equation(30):

Fx=Px 0+Vf×m/n.  (30)

In Equation (30), “n” represents the number of times of processing perunit time, and the counter m is initialized at intervals of one verticalsynchronizing period which is the processing cycle of the processing ofFIG. 24. Accordingly, in a camera which conforms to, for example, theNTSC television system, the counter m takes on the following values:

m=1, 2, 3, . . . , n/60.

Therefore, when m=n/60, the target position Fx becomes:

Fx=Px 0+Vf/60=Px′.

Thus, the focusing lens 105 reaches the position Px′ after one verticalsynchronizing period.

The reason why the value of the counter m is added to the referenceposition Px0 as a variable is to prevent the following phenomenon: ifthe operation of adding the amount of movement Vf/n by which thefocusing lens 105 is moved each time the processing of FIG. 25 isexecuted once to the current position Px of the focusing lens 105 isrepeated, an error due to the characteristics of loop control actuallyoccurs between a target position and an actual position to which thefocusing lens 105 is moved, and such error is accumulated so that theposition to be reached by the focusing lens 105 after one verticalsynchronizing period deviates from Px′.

Accordingly, by determining the target position Fx by using Equation(30), for example, even if an actual position of the focusing lens 105deviates from a target position during the previous movement, the nexttarget position to be calculated is not affected by the previouspositional deviation, so that the previous positional deviation can becorrected.

By repeatedly executing the above-described processing shown in FIGS. 24and 25, not only is it possible to maintain an in-focus state even afterthe passage of one vertical synchronizing period, but also the focusinglens 105 can continue to move at an average compensation speed at whichthe focusing lens 105 can maintain an in-focus state, even within onevertical synchronizing period during which the variator lens 102 ismoving. Accordingly, it is possible to prevent defocusing from occurringduring the vertical synchronizing period.

Seventh Embodiment

A seventh embodiment of the present invention will be described below.

In the following description of the seventh embodiment, reference willbe made to an example in which the present invention is applied to theprocessing of eliminating defocusing which occurs when the variator lens102 reaches a zoom end in the image pickup apparatus 100 shown in FIG.18.

A processing program based on the flowchart shown in FIG. 26 iscontained in, for example, the zooming motor control program 116, andthe processing program is executed by the lens control microcomputer112.

The processing shown in FIG. 26 is similar to that shown in FIG. 31except that Steps S1001 to S1003 are inserted between Steps S206 andS207 of FIG. 31.

FIG. 26 shows one example of the processing of adjusting the speed ofthe variator lens 102 so that a predicted target position to be reachedby the variator lens 102 after one vertical synchronizing period becomesaccurately coincident with a zoom end if it is determined that suchpredicted target position exceeds the zoom end.

In the flowchart shown in FIG. 26, identical reference numbers are usedto denote processing steps similar to those shown in the flowchart ofFIG. 31, and the detailed description thereof is omitted.

First, as described previously, in the processing of Step S206, theposition (predicted target position) Zx′ to be reached by the variatorlens 102 after one vertical synchronizing period is obtained from theabove-described equation (22) (Zx′=Zx±Zsp/(vertical synchronizingfrequency)) using the speed Zsp (pps) of the variator lens 102.

The sign “±” used in Equation (22) indicates different moving directionsof the variator lens 102, and the sign “+” indicates the movement of thevariator lens 102 toward the telephoto end, while the sign “−” indicatesthe movement of the variator lens 102 toward the wide-angle end.

Then, it is determined whether the position Zx′ obtained in Step S206 isgreater than a telephoto-end zoom position Zt or whether the positionZx′ is smaller than a wide-angle-end zoom position Zw (Step S1001). Onlyif the position Zx′ is greater than the telephoto-end zoom position Ztor the position Zx′ is smaller than the wide-angle-end zoom position Zw,the processing of Steps S1002 and S1003 is executed.

If it is determined in Step S1001 that the position Zx′ is greater thanthe telephoto-end zoom position Zt, the above equation (22) is convertedinto the following equation (31):

Zsp=(Zt−Zx)×vertical synchronizing frequency.  (31)

Thus, the speed of the variator lens 102 to be speed-reduced isidentified and set.

If it is determined in Step S1001 that the position Zx′ is greater thanthe wide-angle-end zoom position Zw, the above equation (22) isconverted into the following equation (32):

Zsp=(Zx−Zw)×vertical synchronizing frequency.  (32)

Thus, the speed of the variator lens 102 to be speed-reduced isidentified and set (Step S1002).

Then, the predicted target position Zx′ of the variator lens 102 isreset to the telephoto-end zoom position Zt or the wide-angle-end zoomposition Zw (Zx′=Zt or Zx′=Zw) (Step S1003).

Since the routine of resetting the speed of the variator lens 102 isexecuted as Steps S1001 to S1003 as described above, the position to bereached by the variator lens 102 after one vertical synchronizing periodcan be made coincident with a zoom end, whereby an in-focus position forthe zoom end is set at the predicted target position of the focusinglens 105. Accordingly, even if the variator lens 102 stops movingimmediately after having reached the zoom end, the position of thefocusing lens 105 can be set as an in-focus position corresponding tothe position of the zoom end, whereby it is possible to preventoccurrence of defocusing.

Eighth Embodiment

An eighth embodiment of the present invention will be described below.

In the above description of the seventh embodiment, reference has beenmade to the example in which if it is determined that a predicted targetposition to be reached by the variator lens 102 after one verticalsynchronizing period exceeds a zoom end, the speed of the variator lens102 is reduced so that the predicted target position becomes coincidentwith the position of the zoom end to prevent occurrence of defocusing.In the eighth embodiment, in the image pickup apparatus 100 shown inFIG. 18, the processing of forcedly moving the position of the focusinglens 105 to an in-focus position at the instant when the position of thevariator lens 102 reaches a zoom end is executed in addition to theabove-described processing according to the seventh embodiment, therebyreducing the time period of occurrence of defocusing and also therebycompletely eliminating defocusing due to a calculation error or thelike.

For example, a processing program based on the flowchart shown in FIG.27 is contained in the zooming motor control program 116, while aprocessing program based on the flowchart shown in FIG. 28 is containedin the AF program 113. The processing programs are executed by the lenscontrol microcomputer 112.

The processing shown in FIG. 27 is similar to that shown in FIG. 26except that Step S1101 is inserted between Steps S214 and S215 of FIG.26.

The processing shown in FIG. 28 is similar to that shown in FIG. 34except that Steps S1201 to S1206 are inserted between Steps S504, S506and Steps S505, S507, S509.

In the flowcharts shown in FIGS. 27 and 28, identical reference numbersare used to denote processing steps similar to those shown in theflowcharts of FIGS. 26 and 34, and the detailed description thereof isomitted.

First, in the eighth embodiment, when the variator lens 102 stops at azoom end position, an in-focus position of the focusing lens 105relative to the zoom end position is calculated, and the focusing lens105 is forcedly moved to the calculated in-focus position.

For this reason, during the forced movement of the focusing lens 105, itis necessary to inhibit the processing of setting the position Px′obtained in the above-described manner in Step S213 of FIG. 27 to atarget position for the focusing lens 105.

Accordingly, as shown in FIG. 27, a decision is made as to the state ofa forced movement flag which indicates whether the focusing lens 105 isbeing forcedly moved (Step S1101).

If it is determined in Step S1101 that the focusing lens 105 is beingforcedly moved, the process returns to Step S202 without updating thetarget position of the focusing lens 105 in Step S215.

The value of the forced movement flag is set to a value indicative ofthe state of movement of the focusing lens 105, in the processing ofFIG. 28 which will be described later, and is cleared (=“0”) so long asa instruction to drive the variator lens 102 in a direction in which theposition of the variator lens 102 exceeds a zoom end position is notgiven.

The processing of forcedly moving the focusing lens 105 will bedescribed below with reference to FIG. 28. First, if the processingshown in FIG. 28 is started (Step S501), it is determined whether thevariator lens 102 is in a driven state, according to the state ofmovement of the variator lens 102 which has already been determined inthe processing of FIG. 27 (Step S502). If the variator lens 102 is in anon-driven state, the variator lens 102 is made to stop (Step S509) andthe next interrupt period is set (Step S510). Thus, the processing ofFIG. 28 is completed (Step S511).

On the other hand, if the variator lens 102 is in a driven state, it isdetermined in which direction the variator lens 102 is to be driven(Step S503). If the variator lens 102 needs to be driven toward thetelephoto end, the process proceeds to Step S504, whereas if thevariator lens 102 needs to be driven toward the wide-angle end, theprocess proceeds to Step S506.

In Step S504, it is determined whether the variator lens 102 has alreadyreached the telephoto end.

If it is determined in Step S504 that the variator lens 102 has not yetreached the telephoto end, the above-described forced movement flag iscleared (Step S1201). Then, the driving direction of the zooming motordriver 118 is set to a positive rotating direction and the positioncounter Zx for the variator lens 102 is incremented (Step S505).

If it is determined in Step S504 that the variator lens 102 has alreadyreached the telephoto end, the process proceeds to Step S506, in whichit is determined whether the variator lens 102 has already reached thewide-angle end.

If it is determined in Step S506 whether the variator lens 102 has notyet reached the wide-angle end, the forced movement flag is cleared(Step S1202). Then, the driving direction of the zooming motor driver118 is set to a negative rotating direction and the position counter Zxfor the variator lens 102 is decremented by 1 (Step S507).

After the processing of Step S505 or S507, the logic of a currentfrequency signal is inverted so that a frequency signal corresponding tothe driving speed of the variator lens 102 can be outputted to thezooming motor driver 118 (Step S508).

Specifically, in the processing shown in FIG. 28, since interrupts arecaused in accordance with the driving frequency, the output logic forthe zooming motor driver 118 is successively inverted in Step S508.Thus, a pulse train corresponding to the driving frequency is generated,and the zooming motor driver 118 controls the excitation phase of thezooming motor (stepping motor) 117 in accordance with the switching ofthe logic of the pulse train and the driving direction of the zoomingmotor 118. Thus, the variator lens 102 moves in accordance with suchcontrol.

The processing of FIG. 27 is repeatedly performed during the movement ofthe variator lens 102 until the variator lens 102 reaches the positionof a zoom end.

If the variator lens 102 reaches the position of the zoom end, themovement of the variator lens 102 is inhibited and the focusing lens 105is forcedly moved at a high speed to an in-focus position relative tothe position of the zoom end so as not to allow a photographer to noticedefocusing.

Incidentally, in the eighth embodiment, since a linear motor capable ofdriving the motor 1501 at a high speed is used for driving the focusinglens 105, if the focusing lens 105 is made to reach an in-focus pointimmediately after the stop of the variator lens 102 in accordance withthe loop characteristics of a focusing system, it is possible to preventthe photographer from noticing defocusing.

Specifically, if the variator lens 102 reaches the telephoto end whileit is moving toward the telephoto end, the answer in Step S504 is true.

In this case, the in-focus position Px′ to be reached by the focusinglens 105 when the variator lens 102 is positioned at the telephoto endis calculated as a forced movement target position for the focusing lens105 (Step S1203).

This in-focus position Px′ is calculated by using the above-describedequation (23) with the zoom area V′=s (k=s in the data table TB shown inFIG. 35).

If the variator lens 102 reaches the wide-angle end while it is movingtoward the wide-angle end, the answer in Step S506 is true.

In this case, the in-focus position Px′ to be reached by the focusinglens 105 when the variator lens 102 is positioned at the wide-angle endis calculated as a forced movement target position for the focusing lens105 (Step S1204).

This in-focus position Px′ is calculated by using the above-describedequation (23) with the zoom area V′=0 (k=0 in the data table TB shown inFIG. 35).

After the processing of Step S1203 or Step S1204, the forced movementflag is set to 1 (Step S1205) and the target position of the focusinglens 105 is set to the in-focus position Px′ calculated in Step S1203 orStep S1204 (Step S1206), and a driving signal is outputted to the motor(linear motor) 1501.

Then, the driven state of the variator lens 102 is set to a stoppedstate (Step S509) and the next interrupt is set (Step S510). Thus, theprocessing shown in FIG. 28 is completed (Step S511).

In the eighth embodiment, when the position of the variator lens 102reaches an end of its movable range, the movement of the variator lens102 is brought to a stop in a manner similar to that describedpreviously in connection with the seventh embodiment. However, it isalso possible to adopt an arrangement which brings the movement of thevariator lens 102 to a stop when a photographer interrupts a keyoperation for zooming or the like during a zooming operation.

In this arrangement, for example, a switching of the driven state of thevariator lens 102 is detected, and if it is detected that the variatorlens 102 has changed from the driven state to a stopped state, anin-focus position of the focusing lens 105 relative to the stop positionof the variator lens 102 is calculated, and the calculated in-focusposition is used as a forced movement target value for the focusing lens105.

As is apparent from the above description, even in an arrangement inwhich different actuators having different response characteristics areused as actuators for driving the variator lens 102 and the focusinglens 105, i.e., a stepping motor is used as the zooming motor 117 and alinear motor is used as the motor 1501, it is possible to realize acomfortable zooming operation (zooming) which does not allow aphotographer to notice defocusing even if either one of the motors comesto a stop.

Ninth Embodiment

A ninth embodiment of the present invention will be described below.

According to the ninth embodiment, in the image pickup apparatus 100shown in FIG. 18, the cycle of position control of the focusing lens 105is made short relative to the cycle of position control of the variatorlens 102 so that when the variator lens 102 is stopped, the focusinglens 105 is immediately stopped.

When the variator lens 102 is to be stopped, it is necessary to performfine position control so that an in-focus state can be maintained.

Specifically, not only is it necessary to maintain an in-focus stateeven after one vertical synchronizing period, as in the case of aconventional example, but it is also necessary to maintain an in-focusstate even if the variator lens 102 stops at an arbitrary positionwithin one vertical synchronizing period.

As described above, if a motor for driving a focusing lens is a steppingmotor as described above, the focusing lens is driven at an optimumfocus tracing speed according to the inclination of a cam locus and therate of variation in the position of the focusing lens becomescoincident with the slope of the cam locus so that an in-focus state canbe maintained with respect to an arbitrary position of a variator lens.

In contrast, in a system which provides loop control of the position ofa linear motor or the like, since the moving speed of the focusing lensis determined by the response characteristics of a loop, it is difficultto control the moving speed of the focusing at a moving speed accordingto the slope of a cam locus. However, since the position of the variatorlens approaches an in-focus point within one vertical synchronizingperiod after the focusing lens reaches a target in-focus position,defocusing invisibly occurs for only a short time.

However, if the variator lens stops at an arbitrary position, adefocusing preventing effect due to the movement of the variator lensdisappears and defocusing becomes visible.

According to the ninth embodiment, even in a system which performsposition loop control, fine position control is executed to effectpseudo speed control, thereby improving the quality of zoomingperformance. In addition, the frequency of the control cycle requiredfor fine position control is made much higher than the frequency of azoom control cycle, thereby solving the above-described problem whichoccurs when the variator lens reaches a zoom end or the like and azooming operation is interrupted,

As in the case of the above-described sixth embodiment, for example, aprocessing program based on the flowchart of FIG. 24 is contained in,for example, the zooming motor control program 116, and is executed bythe lens control microcomputer 112.

FIG. 29 is a flowchart showing driving control processing for thefocusing lens 105 which performs a compensation operation according tothe movement of the variator lens 102. The processing shown in FIG. 29is similar to that of FIG. 25 used in the above description of the sixthembodiment, except that Step S1301 is inserted immediately before StepS905.

The processing cycle shown in FIG. 29 is also such that the processingis executed n times per unit time.

A processing program based on the flowchart of FIG. 25 is also containedin, for example, the zooming motor control program 116, and is executedby the lens control microcomputer 112.

Since the processing of FIG. 24 has been described previously, thedetailed description thereof is omitted.

In the flowchart of FIG. 29, identical reference numerals are used todenote processing steps similar to those of the flowchart of FIG. 25,and the detailed description thereof is omitted.

First, as described previously, the destination Px′ to be reached by thefocusing lens 105 after one vertical synchronizing period is determinedby the processing of Steps S201 to 212.

Then, the initializing processing of clearing the counter m to be usedin the processing shown in FIG. 29 is executed, and the current positionPx of the focusing lens 105 is stored in the memory Px0 (not shown)provided in the lens control microcomputer 112 (Step S901).

Then, the amount of movement (Px′−Px) of the focusing lens 105 pervertical synchronizing period is divided by the vertical synchronizingperiod to calculate the compensation speed Vf per unit time (Step S902).

Then, the zooming motor (stepping motor) 117 is driven at the zoomingspeed set in Step S204, thereby moving the variator lens 102 (StepS903). Then, the process returns to Step S202 and waits for the nextprocessing cycle.

While the above-described processing is being executed, the processingshown in FIG. 29 is executed on a processing cycle of n times per unittime.

Specifically, if the processing of FIG. 29 is started (Step S904), adecision is made as to the current state of driving of the variator lens102 (Step S1301).

If it is determined in Step S1301 that the variator lens 102 is in astopped state, the process remains in a wait state.

If it is determined in Step S1301 that the variator lens 102 is indriven state, the counter m which has been cleared in Step S901 isincremented (Step S905).

Then, the target position Fx to be reached by the focusing lens 105 eachtime the processing of FIG. 25 is executed once is calculated (StepS906).

This target position Fx is obtained by a calculating method ofsequentially adding the amount of movement, Vf/n, by which the focusinglens 105 is moved each time the processing of FIG. 29 is executed onceto the reference position Px0 at which the focusing lens 105 was presentwhen an in-focus position after one vertical synchronizing period wascalculated.

Specifically, the target position Fx is calculated by using Equation(30) (Fx=Px0+Vf×m/n).

As described previously, in Equation (30), “n” represents the number oftimes of processing per unit time, and the counter m is initialized atintervals of one vertical synchronizing period which is the processingcycle of the processing of FIG. 24. Accordingly, in a camera whichconforms to, for example, the NTSC television system, the counter mtakes on the following values:

m=1, 2, 3, . . . , n/60.

Therefore, when m=n/60, the target position Fx becomes:

Fx=Px 0+Vf/60=Px′.

Thus, the focusing lens 105 reaches the position Px′ after one verticalsynchronizing period.

The reason why the value of the counter m is added to the referenceposition Px0 as a variable is to prevent the following phenomenon: ifthe operation of adding the amount of movement Vf/n by which thefocusing lens 105 is moved each time the processing of FIG. 25 isexecuted once to the current position Px of the focusing lens 105 isrepeated, an error due to the characteristics of loop control actuallyoccurs between a target position and an actual position to which thefocusing lens 105 is moved, and such error is accumulated so that theposition to be reached by the focusing lens 105 after one verticalsynchronizing period deviates from Px′.

Accordingly, by determining the target position Fx by using Equation(30), for example, even if an actual position of the focusing lens 105deviates from a target position during the previous movement, the nexttarget position to be calculated is not affected by the previouspositional deviation, so that the previous positional deviation can becorrected.

By repeatedly executing the above-described processing shown in FIGS. 24and 29, not only is it possible to maintain an in-focus state even afterthe passage of one vertical synchronizing period, but also the focusinglens 105 can continue to move at an average compensation speed at whichthe focusing lens 105 can maintain an in-focus state, even within onevertical synchronizing period during which the variator lens 102 ismoving. Accordingly, it is possible to prevent defocusing from occurringduring the vertical synchronizing period.

In addition, if the processing cycle of FIG. 29 is made faster than amaximum speed Vzmax of the variator lens 102, for example, if n=3 kHzwhich is approximately three times the maximum speed Vzmax, theprocessing of FIG. 29 can be executed once at the time of a decision asto whether the variator lens 102 has reached a zoom end. Accordingly, atthe same time that the variator lens 102 stops, the movement of thefocusing lens 105 can be stopped while the focusing lens 105 is beingmaintained in an in-focus state.

Accordingly, not only when the variator lens 102 stops at a zoom end,but also when a photographer interrupts a zooming operation by a keyoperation or the like, defocusing does not occur.

Incidentally, since the above-described processing is executed by thelens control microcomputer 112, the lens control microcomputer 112 isheavily loaded due to the high-speed processing. However, because of thecharacteristics of each cam loci, the inclination of the cam loci isunsharp at any focal length other than a telephoto range, and cam locifor different subject distances tend to converge, whereby even if theprocessing cycle of FIG. 29 is made slower than the processing cycle ofthe position control processing of the focusing lens 105 shown in eachof FIGS. 34 and 28, the amount of defocusing is extremely small.

Accordingly, if the load on the lens control microcomputer 112 is takeninto account, it is desirable to optimally set the processing cycle ofFIG. 29 according to the focal length or the like, as by making fast theprocessing cycle of FIG. 29 only near the telephoto end at which theinclinations of the cam loci become sharp.

In each of the above-described fourth to ninth embodiments, although alinear motor is used as the motor 1501 for driving the focusing lens105, the motor 1501 is not limited to the linear motor only and ahigh-speed control system using a stepping motor or the like may also beadopted.

As is apparent from the above description, according to each of theabove-described fourth to ninth embodiments, since there is provided anarrangement in which a driving signal is updated and supplied to anactuator by a plurality of times during a predetermined time period sothat the average moving speed of a movable part during the predeterminedtime period becomes a predetermined speed, it is possible to executeposition control and pseudo speed control of the movable part at thesame time. Accordingly, even in a lens position control system using alinear motor, it is possible to realize a smooth high-speed autofocusoperation according to the shape and size of the hill of a focus signal.Accordingly, even if lens control position is executed with a linearmotor, pseudo speed control is enabled so that comfortable autofocus andzooming operations can be realized.

In addition, since there is provided an arrangement in which a targetposition is updated n times during a predetermined time period by theamount of movement, s/n, at a time with respect to the amount ofmovement, s, by which the movable part moves at a predetermined speedduring the predetermined time period, the actual average moving speed ofthe movable part can be held at a uniform speed. Accordingly, it ispossible to prevent a phenomenon which occurs during a hill-climbingoperation or the like for focus adjustment, such as the phenomenon inwhich the movable part is driven at a high speed in accordance with theresponse characteristics of feedback loop, and when the movable partreaches the target position, the driving of the movable part isimmediately stopped and the repetition of drive and stop appears on thepicture of an image being picked up. Furthermore, if a linear motor isused as an actuator, it is possible to realize an ultra-high-speedzooming mechanism as well as to reduce the size and weight thereof.

In addition, since there is provided an arrangement in which the averagemoving speed at which the movable part moves by the predetermined amountof movement can be controlled even in the case of moving the movablepart by a predetermined amount of movement, such as a wobbling operationin an autofocus operation, it is possible to prevent a visually impairedvideo image, such as that which exhibits a non-smooth discontinuousmotion, due to the repetition of drive and stop of the movable part,which occurs in a moving-direction determining operation or a hill topdetermining operation of the movable part in the wobbling operation orthe like. In particular, even if a subject in an in-focus state and asubject in a slightly defocused state are present in the picture of animage being picked up, as in the case of a wobbling operation which isexecuted near a hill top near an in-focus point, it is possible to lowerthe frequency of switching of the movable part from a driven state to astopped state in the wobbling operation or the like, as by reducing theaverage moving speed. Accordingly, it is possible to realize a wobblingoperation or the like which is not visible to a photographer.Accordingly, even in the case of lens position control using a linearmotor, it is possible to realize comfortable autofocus and zoomingoperations by enabling pseudo speed control.

In addition, there is provided an arrangement in which the operation ofdividing a predetermined amount of movement to progressively move themovable part toward a target position until the movable part completesthe predetermined amount of movement and the operation of moving themovable part toward the target position by the predetermined amount ofmovement at a time are selectively executed according to the amount ofmovement of the movable part to be moved. Accordingly, even if thepredetermined amount of movement is large, by dividing the predeterminedamount of movement to progressively move the movable part, it ispossible to prevent a vibration from occurring when the movable part isnear the target position and eliminate the effect of such vibration on afocus voltage signal, whereby it is possible to prevent a malfunctionduring an autofocus operation or the like. In addition, since there isprovided an arrangement in which the movable part can be forcedly movedat a time according to the amount of movement of the movable part, it ispossible to prevent the movable part from moving past the predeterminedamount, and it is also possible to move the movable part at a maximumspeed within a range in which the motion of the movable part is notvisible, on the picture of an image being picked up. Furthermore, if alinear motor is used as an actuator, it is possible to realizeultra-high-speed zooming as well as to reduce the size and weight of theentire mechanism.

In addition, since there is provided an arrangement capable of varyingthe aforesaid predetermined speed according to the signal level or focusstate of the focus voltage signal, it is possible to realize a smoothautofocus operation which is optimum for any subject.

In addition, there is provided an arrangement which, in a magnificationvarying (zooming) operation, predicts a position to be reached by afirst lens group after a predetermined time period (for example, afterone vertical synchronizing period), calculates an in-focus position ofthe movable part relative to the predicted position, and executesposition control of the movable part so that the average moving speed ofthe moving part becomes a predetermined speed (for example, apredetermined compensation speed) in such a manner that the movable partgradually approaches the in-focus position during the predetermined timeperiod in which the first lens group is moving. Accordingly, it ispossible to prevent a phenomenon in which before the first lens grouparrives at the predicted position in the predetermined time period, themovable part arrives at a focus correction position relative to thepredicted position and defocusing becomes visible by an amountequivalent to the difference between the arrival times of the first lensgroup and the movable part. Accordingly, even in the case of lensposition control using a linear motor, it is possible to realizecomfortable autofocus and zooming operations by enabling pseudo speedcontrol.

In addition, since there is provided an arrangement in which theaforesaid predetermined speed is made equivalent to the moving speed atwhich the movable part moves past the positional difference between thecurrent position of the movable part and a position to be reached by themovable part after the predetermined time period, the movable part notonly can maintain an in-focus state even after the predetermined timeperiod, but also can continue to move at an average moving speed whichenables the movable part to maintain an in-focus state according to themovement of the first lens group even within the predetermined timeperiod in which the first lens group is moving.

In addition, there is provided an arrangement which, in themagnification varying (zooming) operation, during the operation (zoomingoperation) of predicting a position to be reached by the first lensgroup after the predetermined time period (for example, after onevertical synchronizing period) and obtaining an in-focus position of themovable part relative to the predicted position as a target position tobe reached by the movable part after the predetermined time period, themoving speed of the first lens group can be reduced so that if thepredicted position exceeds the movable range of the first lens group,the position of the first lens group after the predetermined time periodbecomes equivalent to an end position of the movable range. Accordingly,it is possible to inexpensively reduce defocusing when the first lensgroup reaches the end position (zoom end), without using a specialcircuit. Accordingly, even if lens position control is executed by usingactuators having different response characteristics, such as a linearmotor and a stepping motor, it is possible to realize a comfortablezooming operation by correcting a deviation between the responseperformances of the actuators.

In addition, since there is provided an arrangement in which when themagnification varying (zooming) operation stops due to the fact that thefirst lens group reaches the end position (zoom end) of the movablerange, the movable part is forcedly moved at a high speed to an in-focusposition relative to the stop position of the first lens group, wherebyit is possible to prevent a photographer from noticing the occurrence ofdefocusing when the zooming operation stops. Accordingly, even if lensposition control is executed by using actuators having differentresponse characteristics, such as a linear motor and a stepping motor,it is possible to realize a comfortable zooming operation by correctinga deviation between the response performances of the actuators.

In addition, since there is provided an arrangement in which, in themagnification varying (zooming) operation, even in a system whichperforms position control of the first lens group, fine position controlis executed to realize pseudo speed control, and in addition, thecontrol cycle of fine position control of the movable part is madefaster than the control cycle of position control of the first lensgroup when at least the position of the first lens group is in apredetermined range. Accordingly, since the movable part can beinstantly stopped in an in-focus state when the first lens groupabruptly stops at an arbitrary position, it is possible to prevent theoccurrence of defocusing while realizing a smooth compensation operationor the like and improved image quality. Accordingly, even if lensposition control is executed by using actuators having differentresponse characteristics, such as a linear motor and a stepping motor,it is possible to realize a comfortable zooming operation by correctinga deviation between the response performances of the actuators.

In addition, in the above-described arrangement, since the aforesaidpredetermined range is set to a long focal length range on a telephotoside, for example, a telephoto end at which the slope of a cam locus issharp, the load on a lens control microcomputer can be reduced, wherebyit is possible to realize a high-quality zooming operation without usingan expensive microcomputer or the like.

In addition, since there is provided an arrangement in which a drivingsignal is updated and supplied to an actuator by a plurality of timesduring a predetermined time period so that the average moving speed of amovable part during the predetermined time period becomes apredetermined speed, it is possible to execute position control andpseudo speed control of the movable part at the same time. Accordingly,even in a lens position control system using a linear motor, it ispossible to realize a smooth high-speed autofocus operation according tothe shape and size of the hill of a focus signal. Accordingly, even iflens control position is executed with a linear motor, pseudo speedcontrol is enabled so that comfortable autofocus and zooming operationscan be realized.

In addition, since there is provided an arrangement in which a targetposition is updated n times during a predetermined time period by theamount of movement, s/n, at a time with respect to the amount ofmovement, s, by which the movable part moves at a predetermined speedduring the predetermined time period, the actual average moving speed ofthe movable part can be held at a uniform speed. Accordingly, it ispossible to prevent a phenomenon which occurs during a hill-climbingoperation or the like for focus adjustment, such as the phenomenon inwhich the movable part is driven at a high speed in accordance with theresponse characteristics of feedback loop, and when the movable partreaches the target position, the driving of the movable part isimmediately stopped and the repetition of drive and stop appears on thepicture of an image being picked up. Furthermore, if a linear motor isused as an actuator, it is possible to realize an ultra-high-speedzooming mechanism as well as to reduce the size and weight thereof.

In addition, since there is provided an arrangement in which the averagemoving speed at which the movable part moves by the predetermined amountof movement can be controlled even in the case of moving the movablepart by a predetermined amount of movement, such as a wobbling operationin an autofocus operation, it is possible to prevent a visually impairedvideo image, such as that which exhibits a non-smooth discontinuousmotion, due to the repetition of drive and stop of the movable part,which occurs in a moving-direction determining operation or a hill topdetermining operation of the movable part in the wobbling operation orthe like. In particular, even if a subject in an in-focus state and asubject in a slightly defocused state are present in the picture of animage being picked up, as in the case of a wobbling operation which isexecuted near a hill top near an in-focus point, it is possible to lowerthe frequency of switching of the movable part from a driven state to astopped state in the wobbling operation or the like, as by reducing theaverage moving speed. Accordingly, it is possible to realize a wobblingoperation or the like which is not visible to a photographer.Accordingly, even in the case of lens position control using a linearmotor, it is possible to realize comfortable autofocus and zoomingoperations by enabling pseudo speed control.

In addition, there is provided an arrangement in which the operation ofdividing a predetermined amount of movement to progressively move themovable part toward a target position until the movable part completesthe predetermined amount of movement and the operation of moving themovable part toward the target position by the predetermined amount ofmovement at a time are selectively executed according to the amount ofmovement of the movable part to be moved. Accordingly, even if thepredetermined amount of movement is large, by dividing the predeterminedamount of movement to progressively move the movable part, it ispossible to prevent a vibration from occurring when the movable part isnear the target position and eliminate the effect of such vibration on afocus voltage signal, whereby it is possible to prevent a malfunctionduring an autofocus operation or the like. In addition, since there isprovided an arrangement in which the movable part can be forcedly movedat a time according to the amount of movement of the movable part, it ispossible to prevent the movable part from moving past the predeterminedamount, and it is also possible to move the movable part at a maximumspeed within a range in which the motion of the movable part is notvisible, on the picture of an image being picked up. Furthermore, if alinear motor is used as an actuator, it is possible to realizeultra-high-speed zooming as well as to reduce the size and weight theentire mechanism.

In addition, since there is provided an arrangement capable of varyingthe aforesaid predetermined speed according to the signal level or focusstate of the focus voltage signal, it is possible to realize a smoothautofocus operation which is optimum for any subject.

In addition, there is provided an arrangement which, in a magnificationvarying (zooming) operation, predicts a position to be reached by afirst lens group after a predetermined time period (for example, afterone vertical synchronizing period), calculates an in-focus position ofthe movable part relative to the predicted position, and executesposition control of the movable part so that the average moving speed ofthe moving part becomes a predetermined speed (for example, apredetermined compensation speed) in such a manner that the movable partgradually approaches the in-focus position during the predetermined timeperiod in which the first lens group is moving. Accordingly, it ispossible to prevent a phenomenon in which before the first lens grouparrives at the predicted position in the predetermined time period, themovable part arrives at a focus correction position relative to thepredicted position and defocusing becomes visible by an amountequivalent to the difference between the arrival times of the first lensgroup and the movable part. Accordingly, even in the case of lensposition control using a linear motor, it is possible to realizecomfortable autofocus and zooming operations by enabling pseudo speedcontrol.

In addition, since there is provided an arrangement in which theaforesaid predetermined speed is made equivalent to the moving speed atwhich the movable part moves past the positional difference between thecurrent position of the movable part and a position to be reached by themovable part after the predetermined time period, the movable part notonly can maintain an in-focus state even after the predetermined timeperiod, but also can continue to move at an average moving speed whichenables the movable part to maintain an in-focus state according to themovement of the first lens group even within the predetermined timeperiod in which the first lens group is moving.

In addition, there is provided an arrangement which, in themagnification varying (zooming) operation, during the operation (zoomingoperation) of predicting a position to be reached by the first lensgroup after the predetermined time period (for example, after onevertical synchronizing period) and obtaining an in-focus position of themovable part relative to the predicted position as a target position tobe reached by the movable part after the predetermined time period, themoving speed of the first lens group can be reduced so that if thepredicted position exceeds the movable range of the first lens group,the position of the first lens group after the predetermined time periodbecomes equivalent to an end position of the movable range. Accordingly,it is possible to inexpensively reduce defocusing when the first lensgroup reaches the end position (zoom end), without using a specialcircuit. Accordingly, even if lens position control is executed by usingactuators having different response characteristics, such as a linearmotor and a stepping motor, it is possible to realize a comfortablezooming operation by correcting a deviation between the responseperformances of the actuators.

In addition, since there is provided an arrangement in which when themagnification varying (zooming) operation stops due to the fact that thefirst lens group reaches the end position (zoom end) of the movablerange, the movable part is forcedly moved at a high speed to an in-focusposition relative to the stop position of the first lens group, wherebyit is possible to prevent a photographer from noticing the occurrence ofdefocusing when the zooming operation stops. Accordingly, even if lensposition control is executed by using actuators having differentresponse characteristics, such as a linear motor and a stepping motor,it is possible to realize a comfortable zooming operation by correctinga deviation between the response performances of the actuators.

In addition, since there is provided an arrangement in which, in themagnification varying (zooming) operation, even in a system whichperforms position control of the first lens group, fine position controlis executed to realize pseudo speed control, and in addition, thecontrol cycle of fine position control of the movable part is madefaster than the control cycle of position control of the first lensgroup when at least the position of the first lens group is in apredetermined range. Accordingly, since the movable part can beinstantly stopped in an in-focus state when the first lens groupabruptly stops at an arbitrary position, it is possible to prevent theoccurrence of defocusing while realizing a smooth compensation operationor the like and improved image quality. Accordingly, even if lensposition control is executed by using actuators having differentresponse characteristics, such as a linear motor and a stepping motor,it is possible to realize a comfortable zooming operation by correctinga deviation between the response performances of the actuators.

In addition, in the above-described arrangement, since the aforesaidpredetermined range is set to a long focal length range on a telephotoside, for example, a telephoto end at which the slope of a cam locus issharp, the load on a lens control microcomputer can be reduced, wherebyit is possible to realize a high-quality zooming operation without usingan expensive microcomputer or the like.

In addition, since there is provided an arrangement in which a drivingsignal is updated and supplied to an actuator by a plurality of timesduring a predetermined time period so that the average moving speed of amovable part during the predetermined time period becomes apredetermined speed, it is possible to execute position control andpseudo speed control of the movable part at the same time. Accordingly,even in a lens position control system using a linear motor, it ispossible to realize a smooth high-speed autofocus operation according tothe shape and size of the hill of a focus signal. Accordingly, even iflens control position is executed with a linear motor, pseudo speedcontrol is enabled so that comfortable autofocus and zooming operationscan be realized.

In addition, if a linear motor is used as the actuator, it is possibleto reduce ultra-high-speed zooming as well as to reduce the size andweight of the entire mechanism.

In addition, since there is provided an arrangement which extracts apredetermined focus signal which varies according to the state of focus,from an picked-up image signal obtained by picking up an image of asubject via image pickup means, and determines the state of focus, it ispossible to realize a smooth autofocus operation which is optimum forany subject.

In addition, since there is provided an arrangement in which a targetposition is updated n times during a predetermined time period by theamount of movement, s/n, at a time with respect to the amount ofmovement, s, by which the movable part moves at a predetermined speedduring the predetermined time period, the actual average moving speed ofthe movable part can be held at a uniform speed. Accordingly, it ispossible to prevent a phenomenon which occurs during a hill-climbingoperation or the like for focus adjustment, such as the phenomenon inwhich the movable part is driven at a high speed in accordance with theresponse characteristics of feedback loop, and when the movable partreaches the target position, the driving of the movable part isimmediately stopped and the repetition of drive and stop appears on thepicture of an image being picked up.

What is claimed is:
 1. An image pickup apparatus comprising: a firstlens group for performing a magnification varying operation; a secondlens group for correcting a movement of a focal plane during a movementof said first lens group; driving device adapted to respectively drivesaid first lens group and said second lens group; storage device adaptedto store, according to a subject distance, an in-focus position of saidsecond lens group relative to a position of said first lens group;predicting device adapted to predict a destination position to bereached by said first lens group after a predetermined time according toa moving speed of said first lens group, during the magnificationvarying operation; and control device adapted to compute an in-focusposition of said second lens group corresponding to the destinationposition of said first lens group and a moving speed of said first lensgroup, and controlling said driving device to drive said second lensgroup at the moving speed so as to reach an in-focus position after thepredetermined time.
 2. An image pickup apparatus comprising: a firstlens group for performing a magnification varying operation; a secondlens group for correcting a movement of a focal plane during a movementof said first lens group; driving device adapted to respectively drivesaid first lens group and said second lens group; storage device adaptedto store, according to a subject distance, an in-focus position of saidsecond lens group relative to a position of said first lens group; focusdetecting device adapted to output a focus signal; predicting deviceadapted to predict a destination position to be reached by said firstlens group after a predetermined time according to a moving speed ofsaid first lens group, during the magnification varying operation; andcontrol device adapted to compute an in-focus position of said secondlens group corresponding to the destination position of said first lensgroup and a moving speed of said first lens group, and controlling saiddriving device to drive said second lens group at the moving speed so asto reach at the in-focus position after the predetermined time whilevarying the moving speed according to an increase or decrease in thefocus signal.
 3. An image pickup apparatus comprising: a first lensgroup for performing a magnification varying operation; a second lensgroup for correcting a movement of a focal plane during a movement ofsaid first lens group; driving device adapted to respectively drive saidfirst lens group and said second lens group; storage device adapted tostore, according to a subject distance, an in-focus position of saidsecond lens group relative to a position of said first lens group;predicting device adapted to predict a destination position to bereached by said first lens group after a predetermined time according toa moving speed of said lint lens group, during the magnification varyingoperation; calculating device adapted to find a correction position ofsaid second lens group for correcting a movement of a focal positionwith respect to the destination position, according to informationstored in said storage device; and control device adapted to control aposition of said second lens group so that said second lens groupreaches the correction position after the predetermined time.
 4. Animage pickup apparatus comprising; a first lens group for perforating amagnification varying operation; a second lens group for correcting amovement of a focal plane during a movement of said first lens group;driving device adapted to respectively drive said first lei~s group andsaid second lens group; storage device adapted to store, according to asubject distance, an in-focus position of said second lens grouprelative to a position of said first lens group; focus detecting deviceadapted to output a focus signal; predicting device adapted to predict adestination position to be reached by said first lens group after apredetermined time according to a moving speed of said first lens group,during the magnification varying operation; calculating device adaptedto find a correction position of said second lens group for correcting amovement of a focal position with respect to the destination position,according to information stored in said storage device; correctionposition changing device adapted to change the correction positionaccording to an increase or decrease in the focus signal; and controldevice adapted to control a position of said second lens group so thatsaid second lens group reaches the correction position after thepredetermined time.
 5. An image pickup apparatus according to one ofclaims 1 to 4, wherein the predetermined time is substantiallyequivalent to one vertical synchronizing period.
 6. An image pickupapparatus according to one of claims 1 to 4, wherein a stepping motor isused as said driving means.
 7. An image pickup apparatus according toone of claims 1 to 4, wherein a linear motor is used as said drivingmeans.
 8. An image pickup method of picking up an image by using a firstlens group for performing a magnification varying operation, a secondlens group for correcting a movement of a focal plane during a movementof said first lens group, driving device adapted to respectively drivesaid first lens group and said second lens group, storage device adaptedto store, according to a subject distance, an in-focus position of saidsecond lens group relative to a position of said first lens group, saidimage pickup method comprising the steps of: predicting a destinationposition to be reached by said first lens group after a predeterminedtime according to a moving speed of said first lens group, during themagnification varying operation; and computing an in-focus position ofsaid second lens group corresponding to the destination position of saidfirst lens group and a moving speed of said first lens group, andcontrolling said driving device to drive said second lens group at themoving speed so as to reach at the in-focus position after thepredetermined time.
 9. An image pickup method of picking up an image byusing a first lens group for performing a magnification varyingoperation, a second lens group for correcting a movement of a focalplane during a movement of said first lens group, driving device adaptedto respectively drive said first lens group and said second lens group,storage device adapted to store, according to a subject distance, anin-focus position of said second lens group relative to a position ofsaid first lens group, and extracting device adapted to extract a focussignal from a signal of an image picked up by image pickup device, saidimage pickup method comprising the steps of: predicting a destinationposition to be reached by said first lens group after a predeterminedtime according to a moving speed of said first lens group, dining themagnification varying operation; and computing an in-focus position ofsaid second lens group corresponding to the destination position of saidfirst lens group and a moving speed of said first lens group, andcontrolling said driving device to drive said second lens group at themoving speed so as to reach at the in-focus position after thepredetermined time while varying the moving speed according to anincrease or decrease in the focus signal.
 10. An image pickup method ofpicking up an image by using a first lens group for performing amagnification varying operation, a second lens group for correcting amovement of a focal plane during a movement of said first lens group,driving device adapted to respectively drive said first lens group andsaid second lens group, storage device adapted to store, according to asubject distance, an in-focus position of said second lens grouprelative to a position of said first lens group, said image pickupmethod comprising the steps of: predicting a destination position to bereached by said first lens group after a predetermined time periodaccording to a moving speed of said first lens group, during themagnification varying operation, finding a correction position of saidsecond lens group for correcting a movement of a focal position withrespect to the destination position, according to the information storedin said storage device; and controlling a position of said second lensgroup so that said second lens group reaches the correction positionafter the predetermined time.
 11. An image pickup method of picking upan image by using a first lens group for performing a magnificationvarying operation, a second lens group for correcting a movement of afocal plane during a movement of said first lens group, driving deviceadapted to respectively drive said first lens group and said second lensgroup, storage device adapted to store, according to a subject distance,an in-focus position of said second lens group relative to a position ofsaid first lens group, and extracting device adapted to extract a focussignal from a signal of an image picked up by image pickup, said imagepickup method comprising the steps of: predicting a destination positionto be reached by said first lens group after a predetermined timeaccording to a moving speed of said first lens group, during themagnification varying operation, finding a correction position of saidsecond lens group for correcting a movement of a focal position withrespect to the destination position, according to the information storedin said storage device; changing the correction position according to anincrease or decrease in the focus signal; and controlling a position ofsaid second lens group so that said second lens group reaches thechanged correction position after the predetermined time.
 12. An imagepickup method according to one of claims 8 to 11, wherein thepredetermined is substantially equivalent to one vertical synchronizingperiod.
 13. An image pickup method according to one of claims 8 to 11,wherein a stepping motor is used as a driving device.
 14. An imagepickup method according to one of claims 8 to 11, wherein a linear motoris used as said driving device.
 15. An image pickup apparatuscomprising; a first lens group for performing a magnification varyingoperation; a second lens group for correcting a movement of a focalplane during a movement of said first lens group; detecting deviceadapted to detect a position of said second lens group; driving deviceadapted to drive said second lens group by supplying a driving signal toan actuator for moving said second lens group along an optical axis;storage device adapted to store, according to a subject distance, anin-focus position of said second lens group relative to a position ofsaid first lens group; predicting device adapted to predict adestination position to be reached by said first lens group after apredetermined time according to a moving speed of said first lens group,during the magnification varying operation; calculating device adaptedto calculate a correction position of said second lens group forcorrecting a movement of a focal position with respect to thedestination position predicted by said predicting device according toinformation stored in said storage device; and position control deviceadapted to perform position control of said second lens group so that,after the predetermined time, said second lens group reaches thecorrection position calculated by said calculating device, wherein saidposition control device controls a movement of said second lens group sothat an average moving speed of said second lens group during thepredetermined time becomes a predetermined speed.
 16. An image pickupapparatus according to claim 15, wherein the predetermined speed issubstantially equivalent to a speed at which said second lens groupmoves past a positional difference between a current position of saidsecond lens group and the correction position calculated by saidcalculating device, within the predetermined time.
 17. An image pickupapparatus comprising: a first lens group for performing a magnificationvarying operation; first driving device adapted to move said first lensgroup; a second lens group for correcting a movement of a focal planeduring a movement of said first lens group; detecting device adapted todetect a position of said second lens group; second driving deviceadapted to drive said second lens group by supplying a driving signal toan actuator for moving said second lens group along an optical axis;storage device adapted to store, according to a subject distance, anin-focus position of said second lens group relative to a position ofsaid first lens group; predicting device adapted to predict adestination position to be reached by said first lens group after apredetermined time according to a moving speed of said first lens group,during the magnification varying operation; calculating device adaptedto calculate a correction position of said second lens group forcorrecting a movement of a focal position with respect to thedestination position predicted by said predicting:device according toinformation stored in said storage device; and position control deviceadapted to perform position control of said second lens group so that,after the predetermined time, said second lens group reaches thecorrection position calculated by said calculating device, a movingspeed of said first lens group being controlled so that a position to bereached by said first lens group after the predetermined time becomescoincident with an end position of a movable range of said first lensgroup if the destination position predicted by said predicting deviceexceeds the end position.
 18. An image pickup apparatus comprising: afirst lens group fir performing a magnification varying operation; firstdriving device adapted to move said first lens group; a second lensgroup for correcting a movement of a focal plane during a movement ofsaid first lens group; detecting device adapted to detect a position ofsaid second lens group; second driving device adapted to drive saidsecond lens group by supplying a driving signal to an actuator formoving said second lens group along an optical axis; storage deviceadapted to store, according to a subject distance, an in-focus positionof said second lens group relative to a position of said first lensgroup; predicting device adapted to predict an in-focus positioncorresponding to a predicted position of said first lens group to bereached after a predetermined time; control device adapted to performposition control of said second lens group for correcting a movement ofa focal position due to a variation in position of said first lens groupduring the magnification varying operation, according to informationstored in said storage device, said second lens group moved a positioncorresponding to the predicted position of said first lens group andforcedly moved to an in-focus position relative to a stop position ofsaid first lens group at the instant when the magnification varyingoperation stops.
 19. An image pickup apparatus comprising: a first lensgroup for performing a magnification varying operation; a second lensgroup for correcting a movement of a focal plane during themagnification varying operation; a first actuator for performingposition control of said first lens group to move said first lens groupalong an optical axis; a second actuator for performing position controlof said second lens group to move said second lens group along theoptical axis so as to reach an in-focus position when the magnificationvarying operation is completed by executing a computation of theposition of said second lens group on the basis of the positions of saidfirst and second lens groups, wherein the computation cycle of saidsecond lens group being made shorter than a position control cycle ofsaid first lens group located at least in a predetermined area.
 20. Animage pickup apparatus according to claim 19, wherein the predeterminedarea is a long focal length area on a telephoto side.
 21. A method ofcontrolling an image pickup apparatus, comprising the steps of: causingan actuator to move a second lens group for correcting a movement of afocal plane during a movement of a first lens group for performingmagnification varying operation; predicting a destination position to bereached by said first lens group after a predetermined time according toa moving speed of said first lens group during the magnification varyingoperation; and calculating a correction position of said second lensgroup for correcting a movement of a focal position with respect to thepredicted destination position of said first lens group, by means of amemory which stores an in-focus position of said second lens grouprelative to a position of said first lens group according to a subjectdistance, and performing position control of said second lens group sothat, after the predetermined time, said second lens group reaches thecalculated correction position, a movement of said second lens groupbeing controlled so that an average moving speed of said second lensgroup during the predetermined time becomes a predetermined speed.
 22. Amethod of controlling an image pickup apparatus according to claim 21,wherein the predetermined speed is substantially equivalent to a speedat which said second lens group moves past a positional differencebetween a current position of said second lens group and the correctionposition within the predetermined time.
 23. A method of controlling animage pickup apparatus, comprising the steps of: causing an actuator tomove a second lens group for correcting a movement of a focal planeduring a movement of a first lens group for performing a magnificationvarying operation; predicting a destination position to be reached bysaid first lens group after a predetermined time according to a movingspeed of said first lens group during the magnification varyingoperation; and calculating a correction position of said second lensgroup for correcting a movement of a focal position with respect to thepredicted destination position of said first lens group, by means of amemory which stores an in-focus position of said second lens grouprelative to a position of said first lens group according to a subjectdistance, and performing position control of said second lens group sothat, after the predetermined time, said second lens group reaches thecalculated correction position, a moving speed of said first lens groupbeing controlled so that a position to be reached by said first lensgroup after the predetermined time becomes coincident with an endposition of a movable range of said first lens group if the predicteddestination position exceeds the end position.
 24. A method ofcontrolling an image pickup apparatus, comprising the steps of: causingan actuator to mow a second lens group for correcting a movement of afocal plane during a movement of a first lens group for performing amagnification varying operation; predicting a destination position to bereached by said first lens group after a predetermined time according toa moving speed of said first lens group during the magnification varyingoperation; and calculating a correction position of said second lensgroup for correcting a movement of a focal position with respect to thepredicted destination position of said first lens group, by means of amemory which stores an in-focus position of said second lens grouprelative to a position of said first lens group according to a subjectdistance, and performing position control of said second lens group sothat, after the predetermined time, said second lens group reaches thecalculated correction position, said second lens group being moved aposition corresponding to the predicted position of said first lensgroup and forcedly moved to an in-focus position relative to a stopposition of said first lens group at the instant when the magnificationvarying operation stops.
 25. A method of controlling an image pickupapparatus which performs position control of a first lens group forperforming a magnification varying operation and a second lens group forcorrecting a movement of a focal plane dining the magnification varyingoperation, comprising the steps of: performing position control of saidfirst lens group by a first actuator to move said first lens group alongan optical axis; performing a position control of said second lens groupby a second actuator to move said second lens group along the opticalaxis so as to reach an in-focus position when the magnification varyingoperation is completed by executing a computation of the position ofsaid second lens group on the basis of the positions of said first andsecond lens groups; and performing the computation cycle of said secondlens group being made shorter than a position control cycle of saidfirst lens group located at least in a predetermined area.
 26. A methodof controlling an image pickup apparatus according to claim 25, whereinthe predetermined area is a long focal length area on a telephoto side.